The first thing to do at the start of the game is start building probes. Pretty much always have one building, but you should never queue them much past 2 (and do that only late game). Next you have to build a pylon (consider walling off by building the pylon so that you may later put buildings at the top of your ramp), do so shortly after your supply reads "9/10." If you like, you may use the probe that built this pylon to scout. While there is a lot you can tell from an early scout (probe #, presence of lack of buildings at certain times), the most important thing is to find where your opponent's base is. When you send an army out later, you only leave your base vulnerable if you attack toward empty high ground. At 13/18 (as a probe is building) add a gateway. Next add an assimilator and another pylon, just make sure that both of these are down no later than 16/18. As soon as the 1st gateway finishes, build your cybernetics core, getting that done quickly is key (you can't build any new buildings or units without it). As soon as you can after dropping the cyernetics core, build your other assimilator. Continue to build probes one at a time (if you queue, you won't have enough minerals to do this fast enough). After the Cybernetics core finishes, build a gateway, but after this, you more or less take your own path. A couple popular routes are to go robo after the 2 gateways (plan on using it for immortals and to get to colossus.....btw, the upgrade for colo is essential when you get them) and then add a 3rd gate, or to add a 3rd and 4th gate (build, and know how to effectively use sentries and their force fields/guardian shield if you plan on having a gate unit-heavy composition, or you'll have a ton of extra gas, and not enough minerals). As one last note, 1 base with a full probe count (26, or 2 full horizontal bars when selected, plus 3 on each gas) can support either 3 gates and a robo or 4 gates. Any extra structures won't be get used enough to maximize their value (or they'll be used and something else you built will be neglected). While you can feel free to experiment with a star gate or templar/DTs, instead of the robo, I've found that it takes a lot of skill to do anything effective with these units early game (considering how their cost effects what gateway units you can build).
1) Void ray rush: Get your Cy-core up before your first zeal and then a stalker+stargate. Pump voidrays out with chrono boosts. Get another stargate if you want.
2)Cannon rush: Wall off your choke with a pylon and forge, and send your probe to the enemies' base and start creating pylons and cannons near their main base. No gas needed.
3)DT rush: Wall off well and rush to DT tech. Get an observer and warp prism as well. Get at least 4 gateways. Send warp prism to side of enemies' base without them noticing. Warp in DTs and aim for their workers/units.
4)Probe rush: Send all your 6 probes at the starting of the game and attack the enemy. With expert micro you can pull this shit off.
5)Mothership rush: Wall off and tech up to the Mothership immediately. Chornoboost it out, and try to get at least 1 or 2 carriers with it. You will probably be left with these units as the enemy wipes out your base, but with these units you will win. Probably.
6)Zeal rush: Get 3 gateways and Warp-in tech. Spam zeals and attack enemy. Start attack when you have about 15 zeals.
7)Pheonix Harass: Tech to pheonix as soon as possible. Get about 2 stargates. Send 4 pheonixes to enemy and piss off his workers.