Stick to the simple units. I play Protoss and some of the biggest mistakes I see out there is with people teching up too quickly and leaving themselves defenseless. In the beginning of the game you need as much protection as you can. If you tech up all you have is a few fancy buildings while the other person has a ton of units. And teching up includes upgrading your units. In the beginning of the game you need to worry about getting out as many units as you can so forget about building that Forge and upgrading your attack until the mid game. I open with a 4-gate build for most of my games, unless I scout the other person and see them going for something that will make that more difficult. Throw in an Assimilator after your first Pylon and start getting some gas. After that throw in a Cybernetics Core right after your first Gateway. By the time the Cybernetics Core is done building you should have a good gas store and you want to immediately get the warp gate upgrade. And don't forget to spit out some sentrys! They are a must in the opening game.
The key here is to stick to Zealots, Stalkers, and Sentrys in the opening game. If you don't knock them out then tech up. If they go air then you might want to spit out more Stalkers or go Void Ray. If they go ground then make more Zealots, add some upgrades and get some Immortals.
Hope that helps and I hope to see you on there! I'm playing the Beta and man is it epic! I took an entire week off work in March for the release.