For the Protoss, base layout is key. Place your pylons so they power your buildings but don't clutter your base, and put imprtant tech-tree structures close together in a very protected area.

 Protoss Probes don't have to wait around to "build" a structure. They can simply open the Warp Rift and move on. This allows you to use all but one of your probes for harvesting resources.

 Gas it up! More than any other race, the Protoss rely on Vespene Gas to build their high-priced units. Move to secure multiple Vespene Geysers whenever possible.

 Although Photon Cannons are an excellent defensive structure, they're fairly expensive. Build them in groups so they can support one another; then make sure build more than one Pylon to service them. As a rule of thumb, build 2 Pylons for every 6 Photon Cannons.

 Have an Arbiter follow a unit in the group it's covering with it's cloak. This way, the Arbiter, although never actively engaged in combat, will follow just behind the attack force.

 Use the High Templar's Hallucination ability. When attacking any large force, keep a good mix of hallucinated units in your front line. Done properly this can give you a huge advantage, because the enemy will waste many of their defensive attacks on units that don't exist.

 Throw a Templar or two in a shuttle and move them to an area just behind an enemy mineral field. Then have your Templar's use Psionic Stormon the streams of enemy workers that approach to collect resources.

 Put an Observer over each unowned mineral field. When the enemy comes to set up a base you'll know, and you can take it out before it's established.

 Fly an Arbiter behind enemy lines and have it use it's Recall ability to bring in a group of Archons. Sit back and survey the carnage..

 If you use Carriers, make sure you upgrade the capacity before you take them into battle. The difference between a non-upgraded Carrier and an upgraded one is considerable, so it's worth waiting until you've completed that technological advance.

 Large groups of Carriers are very powerful, but it's important to keep an Observer with your Carrier groups so you can spot cloaked Wraiths.

 In multiplayer games, be prepared for a Firebat rush. A combo of Zealots, Dragoons, and Photon Cannonsare your best defense. Zealots alone are generally insufficient.

 Against Goliaths, Zealots are your best unit, but make sure you have their speed upgrade before you try to chase one down. As with nearly all units, it's important to attack in force if you're pitting Zealots against Goliaths.

Beware of Science Vessels. An EMP used properly against your forces can rob you of your shields (until they regenerate). For this reason it's good to keep your units spread out .

 Against Battlecruisers, use a combo of Carriers and Scouts. Try to outnumber the Battlecruisers. Ideally, you'll get a couple Arbiters to cloak you're units while you attack.

 Keep a couple Observers patrolling the base perimeter to check for cloaked Wraiths or Ghosts preparing to nuke.

 Don't allow Zerg Overlords to hang around your base. Build Dragoons to chase them away. Photon Cannons aren't always effective for this because the Overlords will simply fly out of range. Never let the enemy know anything they don’t have to know.

 Zerglings can destroy Photon Cannons quickly, so make sure you have other troops handy to support your Photon Cannons in case of an all-out rush.

 Try to keep an eye on all units in your base. If a unit has caught parasite, use it against the enemy. For example, if a Zealot has been infested with a parasite send it with a few other units on an attack run against an auxiliary Zerg target (such as a small outpost) while you send in a real attack force against the Zerg main base. Often the Zerg will pull defenses toward the outpost, leaving the real target undefended.

 Mutalisks can be very effective against the Protoss, so build plenty of Dragoons and Scouts to defend against them. If a large group of Mutalisks attacks, counterattack with a greater force or you may lose a lot of your troops.

 Reavers are fantastic for attacking Zerg bases. Their Scarabs can decimate Zerg structures quickly, because Zerg bases are usually smaller and more efficient.

 If the enemy is using a lot of Zerglings against you, counter with Zealots. The Zergling's small size makes them difficult to target, so use "Attack-Move" commands to get the Zealots into mop-up mode.

 The Scourge makes the Carrier a bad investment against the Zerg. A Carrier can cost up to 950 in resources and be destroyed by as few as five or six Scourge. That's one bad trade.