1) Misuse Removal on My Own Turn
Back when Magic was new, the best card was obviously Lightning Bolt. Okay maybe it wasn't the best card, or even the best boon, but for my money (which was not much in those days), it could kill nearly as much as Terror (who pays $.50 to $1 in the secondary market for Swords to Plowshares, especially with that drawback?), and could go straight to the face. Given that prior to our discovery of the DCI rules, we played, oh, I don't know, seven or more Lightning Bolts in a deck -- nearly the full 10% of a finished product -- it went to the face often.
The single most important forward movement in my development as a player was realizing that I could wait until the end of my opponent's first turn to Lightning Bolt him, rather than just sending three as soon as I played my first land. It took a while for me to figure out that I should hold the Lightning Bolt for his fellows... as a cheap instant, I could always hoard it and spring the burn later.
I think most players take a minute to fall in love with the additional versatility of instants (versus sorceries) but then go a little overboard as to how and when they exercise the instant's spread. Case in point, using removal on the opponent's turn, or more specifically, during the opponent's combat, once they figure out that is an option.
Misusing removal on your own turn is actually a really high level mistake, and one that I will probably continue to make in about 1/5 of situations, with it being a better-than-average if not optimal use of resources the balance of the time. Unless you need the opponent to over-commit to really sting him on his turn, or you need a desperate amount of card advantage or tempo because you are really far behind, I think it is generally right to spend point removal on your own turn, preferably when his mana is tapped... But the right play varies from game to game, stack to stack, uniquely in every unique situation. There is no general rule that covers the gamut of tournament experience. Here are two things that you should think about given the climate of the present Time Spiral Block PTQs:
1a. Pongify - I was playtesting with #1 Apprentice elect Asher "ManningBot" Hecht last night and got very excited that my Foresee gave me a pair of Tendrils of Corruption. I immediately spent them against his Tarmogoyf and Riftsweeper; neither stuck. In one case, ManningBot nuked his own fellow with a Psionic Blast so that I wouldn't gain twelve or so life. Thinking the coast was clear, I ran the next... into a Pongify. If I had waited until Asher's upkeep, I wouldn't have lost to a 3/3 on his turn.
1b. Running test spells on the opponent's upkeep has been a widely practiced technique against Blue since at least 1999. Usually you want to play spells at the end of the opponent's turn if you want to resolve something (which might be the next card), and you play spells on the opponent's upkeep if you don't care if it resolves... but he has to. In Time Spiral Block, more than in Standard, the permission sucks, so you can bleed three or even four mana on the opponent's upkeep with must-counter test spells... Or you can just prevent yourself from losing to a Pongify. Note that playing this way you still deny the opponent the option of his turn's draw, which will greatly affect his ability to respond and the quality of his response.
2) Mana Efficiency Overload - the Paul Sligh Frankenstein's Monster
I am lucky enough to live in Manhattan, New York, generally considered the greatest city in the world. This has numerous advantages, not the least of which is easy access to the strongest sustained pool of Magic talent the game has ever seen. You can't really walk five feet around here without hitting a Pro Tour Champion, and the office is crawling with lowly Grand Prix Champions.
One of the big upsides is the ability to have one's game critiqued on a regular basis, pretty much regardless of who you happen to be playing with at the time. Particularly during drafts, I feel as though I have benefited quite a bit from the opportunity to walk through individual plays. One example that sticks out was functionally the question of playing a Grizzly Bears or a Gray Ogre on my turn (I don't remember the exact cards but for form's sake, these 2/2s were the equivalent). The creatures were about as good as one another; Scott McCord, who was hanging over my shoulder, instructed that I play the Gray Ogre, citing Gray Ogre over Grizzly Bears as essentially the same play, but more mana efficient (the next turn maybe I could run the Grizzly Bears and leave [more] defensive mana up, or make two plays... making the most mana efficient plays preserves your options over the course of a game as it develops).
In fact, the notion of spending as much mana as possible on your own turn, as your mana develops, is probably the second most important lesson any competitive Magic player learns (after comprehending the inherent sauce of the two-for-one). It is generally right to maximize your mana consumption, just like it is generally but not always right to blow up the opponent's threats on your own turn. The problem arises when you take this ideal to the extreme.
In a must-win Regionals match three years ago, I once had twelve lands out. Yes, that's a lot of land! The match-up was my G/W deck versus Tooth and Nail splashing White for Decree of Justice and Wrath of God. He had a couple of worthless creatures in play... maybe some Solemn Simulacrums or Soldier tokens. I was overtaken by how novel it was to have twelve lands in play that I ran a Wrath of God, then hard-cast Akroma, Angel of Wrath, and sent for six. The gigantic problem with this play was that I didn't have to play the Wrath. In fact, my opponent had to deal with Akroma, and was forced to play his own Wrath of God the next turn. I was so swept up by the fact that I could actually Wrath and also play a gigantic Akroma that I didn't realize that I didn't have to do that. In the end, I lost to his third Decree when I found myself bereft of Wraths.
You can avoid this sort of mistake in two ways. The first and better way is to keep focused. Do what Jonny says and concentrate only on what matters; if I had stayed focused, I would have realized that his creatures were not going to have raced my Angel. The second is to pour ice water into your veins. If you are unaffected by how cool something might be (like spending twelve mana, capped off by the deployment of the most gigantic and dangerous girl in Dominaria), you are less likely to fall for the seduction of something ostensibly cool but actually awful (any sub-optimal play is awful compared with the best one).
3) Who is the Fish at this Table? Taking the Bait
Any situation that presents conflicting incentives can give rise to a good bluff, and any interaction at all between two people gives one of them the opportunity to waltz the other through whatever hoops he likes by dangling whatever shiny objects before him happen to be available. However in Magic we have very specific goals almost hard-wired into our brains from our first whispers of card advantage. We often look for the two-for-one and, as with number two, above, can lose sight of what is really important. A clever opponent can use our patterned behavior against us to trick us into bad play that looks so much like good play.
Believe it or not, in the late 1990s there was a debate among the members of Cabal Rogue about whether or not Control should play permanents. Really! This debate could never occur today because people don't play main deck reactive cards, and -- excepting Ancient Grudge in modern Extended -- therefore can't really overload on strategic point removal. However in those days, it was not uncommon for White decks to play five or even six Disenchant-equivalents for Nevinyrral's Disk, maxing out with Divine Offering and Aura of Silence over three games. One camp, exemplified by Mike Donais following a tradition laid out by Jon Finkel, Erik Lauer, and Brian Schneider before him, often held to playing no permanents (Mike didn't count Wall of Blossoms, which replaces itself). The other camp believed that there are some permanents worth playing (Adrian Sullivan has always loved Sylvan Library); John Shuler would routinely demonstrate how to bleed an opponent out of point removal. He would typically lay down Howling Mine, and another Howling Mine, showing the naked two-for-one, then another, maybe some Diamonds... and all of a sudden, the opponent would be stuck under Winter Orb and possibly Icy Manipulator. The opponent would be so excited about breaking the "symmetrical" Howling Mine after netting a free draw card that he would miss the fact that exhausting his elimination, even at card advantage, would leave him defenseless against the subsequent "symmetrical" Winter Orb.
Just the other day, I found myself the embarrassed recipient of a pocket full of bait.
It was a sideboarded game against Pickles, so I had Spell Burst in from my four-color control board. In this match-up, Spell Burst generates a quick one-for-three mana advantage and is highly synergistic with a critical mass of four-mana card drawing with Prismatic Lens and Coalition Relic; if you can get the buyback, buy! In this game, my first Spell Burst got a quick two-for-one on Vesuvan Shapeshifter, and the opponent hung back to rebuild. A few turns later, he presented a face-down, which I met with Spell Burst + buyback... Which is exactly what he wanted. I was tapping my mana to stop non-relevant Morphs. He took the opportunity to play some more morphs... One of them was a Vesuvan Shapeshifter, the other, a Brine Elemental. Defending the combo was not difficult as I had over-spent so much and he had more permission.
How do you avoid making this kind of mistake? After all, we train ourselves to look for certain classes of threatening cards, and in the case of either Disenchantor Spell Burst, the sideboard cards seemed to be doing their job. Well, first and foremost, it is a mistake to deviate from the plan. If you have your plan in mind, and you know what kind of situations to avoid (not just to keep a look out for a certain type of permanent), you will have a better chance. In the case of the artifacts Prison deck, looking for naked two-for-ones might give us some immediate gratification, but the real goal is to not get locked down by mana control... Play accordingly. Same deal on the Spell Burst fumble. Pickles wants you to tap lots of mana and strand your limited reactive cards. Making a target look good is their way of having you play into the plan.
4) The Professor - "He hasn't got it." ... He's got it!
So when a similar situation came up in the second game, when I was way ahead, I told myself "He isn't going to get that lucky two games in a row! Take it." His Kokusho connected for five. His other Kokusho peeked in from his hand just long enough to put me away. I could have blocked the Kokusho attack with Blinkmoth Nexus or fried the Dragon out of the sky, but I wanted to be able to win on my next turn with Shrapnel Blast and Beacon of Destruction... Instead, I didn't get to win at all.
Even if it seems improbable that the opponent has exactly the out he needs to beat you, sometimes he has it. If you get really good at reading your opponents, like Jon Finkel or Bob Maher, you can tell when he has it and can act accordingly. One thing that the really great players keep in mind essentially at all times, is how can he beat me? Maher in particular was a master of this style of play. He was a king of inaction. Bob would do nothing but ride the flow of the opponent's desperate plays if he was ahead, never committing resources if it meant the opponent could piggyback a mistake or over-commitment to win; thus, he held leads until he could win on a lightning strike. Conversely, if he identified a situation where the opponent could win, albeit unlikely, he would defend against that one possibility but block out any other "noise" that was distracting him from the tight execution of his own plan. It sucks, but sometimes the other guy has got it. The trick is knowing when to defend against the improbable situations if you have to versus getting tangled up in your own forward momentum. Look back at my not blocking Kokusho... I was so enamored with winning the next turn that put myself in a spot where I couldn't.
From the other side of the table, when you're behind, you have to identify that one topdeck that you can make to send your opponent off crying and whining about how lucky you are. The tightest play can look like luck, but in fact, the great players are preparing to get lucky where lesser players lose hope and figure they can't win at all. They don't identify these narrow "I can't believe I got there" situations and therefore can't take advantage of them when they come up. Kai Budde topdecked the last Donate in his deck to beat Darwin Kastle after Crosis, the Purger had knocked his hand away. Kai played Illusions of Grandeur previously, putting himself in a spot where he could get lucky. In the same way, Craig Jones, desperate on his heels against Olivier Ruel's Orzhov army, gave himself a chance to win on maybe the most famous topdeck of all time, the $16,000 Lightning Helix.