I assume Affinity does not get much help in the new set, and hopefully there may be a decent hoser for the dominant deck to replace the departing Akroma's Vengeance. Judging by the cards that have been previewed on magicthegathering.com, there should be some shiny new bullets for Tooth and Nail to chamber. Yosei, the Morning Star, and the new legends rule leap to mind immediately. If you Tooth and Nail a pair of these legends into play, they will both be destroyed and you can tap ten permanents your opponent controls AND make them skip two untap steps. It is the green Time Warp.
There will be hundreds of new cards for players to tinker with in their laboratories. Eighth Edition cards will be dusted off to look for interactions and Mirrodin block will be mined for hidden treasures. I know I always look at each new set in the hopes of finding a competitive use for Intruder Alarm and Grave Pact.
The next constructed Pro Tour uses the Extended format, and the hoi polloi will be busying themselves with looking for synergies in the new set to help them dominate that environment. In the meantime, you can get yourself busy with trying to reach that level of play through the PTQ ranks. This weekend's Prerelease is the same format as the next round of qualifiers and should serve as valuable practice. I have always found I do well in the early PTQs of the new Limited season--something I attribute to playing with the set extensively in the opening days of those seasons.
You will have to relearn everything you have adapted for Limited play over the past year. Suddenly you are going to be playing with cards that have colors associated with their mana costs in almost every slot of your deck. Greater attention must be paid to not only the overall mana count of your deck, but how much mana of each color you play as well.
The Prerelease is an excellent opportunity for you to play around with those equations. Don't be afraid to ask questions either. Find out what your opponent's mana was like after the match. Most players will gladly share that information as they are trying to learn the new set as much as you are. I find that Prereleases can often become ‘think tanks' for the new set, with tables of players dissecting mana counts, curves, the viability of splashing colors, and any number of other topics.
I know that going into the event I am planning on playing with at least seventeen lands and possibly eighteen in my forty-card sealed deck. While I would almost always play sixteen and occasionally as low as fifteen lands in Mirrodin, I don't want to skimp on lands until I know if the set can accommodate my stinginess. In Mirrodin you had Talismans and mana Myr to justify the lower mana count. Obviously, if you find there are multiple mana creatures in the new set, you can adjust your mana accordingly.
While getting to six mana seems like a reasonable aspiration to have in this format, the real issue is going to be getting your mana correct in each color. Between playing almost exclusively with artifacts in Mirrodin and then playing with Sunburst cards in Fifth Dawn, most players haven't seen traditional mana in a sealed deck in over a year. Going into the Prerelease you should strive to keep your deck as close to two colors as possible. Generally, I try to play with the two colors that have the best creature curve, and then if I need to add a color with removal, I will 'splash' that color.
By creature curve I mean that you want to play decent creatures from turn one through six using all your mana each turn. While you don't care so much about turn one, you really want a two drop on turn two, a three drop on turn four, etc. From there you need to make sure you will have the colored mana you need to cast them. Many players will count the number of cards they have in each color and try to guesstimate their lands from there. One player I know would actually count the pips--colored mana symbols--on his cards, divide that number by two, and add one to determine his mana. For example, if he was playing green and when he added up the pips in the green cards he was playing it came to sixteen, he would want to play with nine Forests in his deck. If he found that his colors were unbalanced, he would then try to cut out more color-specific, mana-intensive cards until his formula worked.
What is nice about using that formula is that it accounts for cards with multiple colored mana requirements. Fangren Hunter requires more green in your deck to reliably cast on turn five than Tel-Jilad Archers. Simply counting your green cards would not account for that situation. I do not know how he arrived at this formula, but it has served me and a number of other Neutral Ground players admirably over the years. Do not let this trick you into playing a splash card with a double color in the casting cost though. Playing two Plains would not allow for you to play Altar's Light. Cards with two colored mana symbols in the casting cost are generally considered unsplashable.
I remember when Odyssey block came out after the five-color madness of Invasion block and players struggled to readjust their mana bases to more traditional color requirements; I expect that the shift from Mirrodin to Kamigawa will require a similar adjustment. If you plan on playing in the upcoming PTQ season, then this weekend could represent a valuable opportunity to get your game up to that level--Magic's equivalent of baseball's Spring Training.
Good luck this weekend. Here's hoping you open well, build correctly, and have fun!