Just the basic stuff. Make sure you have a good mana curve, a deck full of 1 drops or 5 drops will lose to a deck with a good spread of 2-4 drops. Try to make sure that you don't spread colours too thin (for example, if you want to play a card with a cost of BBB you might need to think about how often you'll actually have three Swamps - if you're playing mainly R/W adding B just for one or two cards might be out of the question)
You can look up primers for the prerelease, depending on how deep you want to go. Look over the set if you get a chance, get a feeling for what the colours of the set do (for example, R/G has some powerful energy cards, and red/white seems to like vehicles) so you won't be overwhelmed when you crack your packs and start looking for what you'll be able to do.
Most importantly, have fun! Limited is my favourite format and if this is your first time don't stress about making a top-tier deck.