Of course you've already read Mike McArtor's Prerelease Primer, right?
And unquestionably you've watched the first Hero's Path video from LoadingReadyRun, an arc that will run through the entire Theros block?
Here are a few other things that will be good for you to know:
1. You can get your color's God in your Seeded Booster. As with the previous Seeded Booster packs in Prerelease kits, there is a chance that you'll get your color's God in your pack. But you won't get any other mythic rare. Also, your Seeded Booster pack isn't entirely your chosen color, it's also cards that might support you if you include one or more other colors.
2. You can play with your Prerelease promo. You will again be able to play with your promo in your Prerelease deck! So don't hesitate to shuffle in the foil-y goodness!
3. You must have fun. This is not optional. It is a requirement. You. Must. Have. Fun. Magic is fun! You should have fun playing it!