Carriers And Zealots
Attack from the sides with carriers and use zealots to attack your enemies base also. If your opponent has defense on the entrance, such as tanks, bunkers, cannons, or sunkens, command your carriers to take them out. After their defense is demolished, fully upgraded zealots can kill bases fairly fast. Get a few arbiters if needed.
The Reaver Drop
Make sure your opponent doesn't have any side defense. If they don't, you can drop reavers without loosing shuttles. You would need a number of shuttles unless you decide to recall reavers. When you do drop/recall, do it behind enemies mineral mining operations. It is a good idea to take out their workers and then attack your enemies. They wouldn't be able to build much. If do not get enough reavers, get some dragoons for backup.
You can use this strategy with other units but I prefer dark templars. This might just work against carriers, battlecruisers, and large units that enemies cant get much of. First, get upgraded arbiters and upgraded dark templars. After you get em', send your arbiters off and freeze carriers, battlecruisers, or any large units they they have. Then recall dark templars in front of their workers. If they got massed units besides carriers or battle cruisers, this strategy might not work.
Power Of High Templars
Really simple strategy. Just drop a lot of templars, get about 20 to drop in front of workers. Then shock em'. After you run out of energy, merge them into archons and kill them from the inside. This works better on money maps, because templars cost a lot of gas. After your archons are merged, get some other units and attack the enemies.
Know Your Protoss Units
The Protoss has the strongest units as they are protected by energy shields that heal quickly. However; once the Protoss buildings themselves are damaged, they cannot be repaired.
Protoss Tactics - Slugmobile Care
Reaver beware. There's a reason these units resemble slugs--they act like them. These slow-moving bad boys require your constant attention, especially in battle. Like the Carriers, you must monitor this unit's supply of ammunition and rebuild it. Plan accordingly by arranging battles that use both the Reavers and the Carriers in one section of the screen. The awesome combined firepower of these two unit types can make short work of almost any enemy installation and you can quickly manufacture more units for both as the battle rages. If you have to zip between raging battles on separate sides of the map, high-maintenance units like the Reaver are going to end up acting as convenient targets for your enemies while they await your resupply commands.
Protoss Tactics - Hog the Resources
Quickly scout the area for other resources. Defending these resources, particularly early in a multiplayer game, is easier than you may think. Your Zealots are amazingly powerful as a first combat option and can easily handle the best of the other races' ground troops. Defend new resource-rich areas with a handful of Zealots and a photon cannon or two and you'll have no problems whatsoever. In the time it takes your opponents to get airborne (the Zealots' main fear), you should have better defenses in place.