I haven't been able to participate in a Pre-Release (or similar Limited Format event) in almost 10 years, so take this advice with a large grain of salt. The biggest issue is the introduction of the "Evolution" Pack; last I knew this was still a "thing", and it should make it much easier to build a coherent deck.
Apart from that, remember that it is four prizes and 40 cards, so once four Pokémon are down you're done, 10 Energy is a fourth of your deck instead of a sixth (but Energy requirements may mean you'll run a higher percentage of Energy than usual), etc. Draw power is usually at a premium, as are search effects (unless too narrow in scope). You can have too many of these things, but it is unlikely. Retreating becomes more important, as your opponent cannot easily force something from the Bench back into the Active position. Special Conditions become more important because shaking them is much more difficult. Colorless attacks become more important because even though you'll probably run two basic Energy Types (possibly even three or four!) they're just easier to fill. Recycling effects matter more because they give you a second chance with something you probably have very few copies of in your deck. Big basics become even better here because Evolutions are likely scarce. Plentiful Evolutions - stuff that is normally filler - can be might here because quantity sometimes equals quality. Off-Type splashes are often important because most decks cannot deal with Weakness exploitation, and even Resistance is more likely to matter here (depending on the set).
Oh, and be wary of +39 decks, sometimes called Mulligan Decks. It is a legitimate strategy for a pre-release, even though some folks seem to think it was invented just a few sets ago. XP If you pull a really great Basic Pokémon, or a Basic and Evolution(s) where the former can search out the latter, as long as said Basic has enough HP to last you can build your entire deck around it. Having just it ensures you open with it, even if your opponent gets a massive amount of mulligan draws. Make sure that the deck is mostly Energy; you must have at least one in hand to keep powering up your Active ASAP. With an opening hand of seven (+1 for drawing, -1 for your Active), that means you only have room for six Trainers. You can risk more if some of them are search or draw, but be careful.
Addendum: Sorry to be so messy about it, but just as I was rushing when I wrote the above text, I need to quickly add circumstances specific to a particular expansion can make certain cards important even if you can barely make use of them. The best example is Stadium cards; while you would obviously include one that benefits you or hurts your opponent, one that is functionally neutral or even less detrimental to you than beneficial to your opponent can be a game-changer.
