The Infamous 4-Gate (Protoss)

Build Order
-9 Pylon
-12 Gateway, Cybernetics Core when Gateway finishes (zealot if you think you need it for blocking or whatever
-14-15 Assimilator
This is a standard Protoss opener. Learn it!
----------------------------------------------------------
As soon as CyberCore finishes, begin warp gate technology. Keep building probes! If you want a more economic route, chrono boost probes. If you want a faster more aggressive 4-gate, chrono boost the warp gate technology instead.
Get your 2nd gas as needed. If you think you are going to need mostly zealots and stalkers, gas_2 might be later, if you need sentries for GS and FF, get 2nd gas earlier.

The big thing you want is to have all 4 gateways done or finishing as your warp gate technology finishes. Place a proxy pylon hidden near your opponent to quickly reinforce your army.

You can constantly produce from all 4 warp gates, so in all likelihood you will beat your opponent with the first attack around 50-60 food. If not, take your natural expansion and add on some upper tech to deal with his army composition.
-------------
Scouting

This build has a natural weakness to Roaches, it is vital to gauge the timing of any Roach Warren and any expansions. Roaches on the field will create problems for a 4 gate attack, and unless the zerg takes a fast expansion, it is unlikely that an overwhelming numerical advantage can be had from 4 gates.

Prioritize Stalkers if you scouted Roaches or a heavy investment in Spine Crawlers, otherwise prioritize Zealots to deal with high Zergling counts. A Sentry or two is always useful to deny mobility or reinforcements to the zerg with force fields.

Aim to do significant economic damage, killing drones or queens, or snipe an expansion. Accept losses to destroy a Hatchery, a units worth in drones, or tech building but do not overcommit in the event that the zerg has heavily defended his main base.

Make sure you scout! A weakness of this is that you won't have an observer out faster than they can get a cloaked unit to you. If you see them going down a tech path that has potential for cloaked units, get that robo and observer out. If you catch it early enough, go for a 3warp gate 1robo build instead.

This strat will get you into diamond easy. There are top protoss diamond players who do nothing but 4-gate very effectively.
See you in the diamond guys.