Part 1: Ground Units

The Protoss units are usually able to take and give more damage than the other race's units. The strength of the Protoss lies in their power in few numbers, which makes organizing attacks easier. Their weakness is in their inflexibility in the tech tree and their great expense. After making Zealots and maybe a few Dragoons, the Protoss player is forced to make a decision to go for Shuttles/Reavers, Templars/Archons, or Scouts/Carriers. You need excellent recon to determine which way to go. Once you have an expansion you can have more variety which you will likely need if the game lasts very long. Never think about making Arbiters or Carriers until you have expanded.

Units and Important Structures:

Shield Battery: These are very important for most all of your games. Build them a considerable amount of time before you need them since it takes time for their energy to fill. They are best used with units with far/ranged attacks like Carriers.

Pylons: They are prime targets during an attack. Have more than one pylon supporting your important structures always. I often used farms in WarCraft 2 as scouts of a sort. The pylon is also useful in this way. Once you have your basic ones established, occasionally use new ones placed far in front of your base entrance to alert you of oncoming threats. Later in the game, you can build one at each resource collection to alert you of expansions. They are better than farms since farms in WarCraft 2 cost wood, while pylons only cost minerals, the more abundant resource.

Photon Cannons: They are good for spotting cloaked/burrowed units (especially spider mines) and in late game they are powerful in huge bunched numbers. They don't have many hit points and don't fire quickly, but they can hit air and ground units (they have the exact same range for both ground and air, although if an air unit moves away at high speeds the cannon will not miss… making it's range seem great). Use them mostly to slow down enemy attacks so you can get important troops there in time.

Probe: The probe is your best early scout. They are your typical worker, except for the fact that they are very small and can leave a building while it is being warped in. One probe is often enough to start a new expansion, but when your opponent has Mutalisks, you had better bring about three probes with Dragoons or Archons for backup. Probes can't be Broodlinged and do not set off spider mines… so use them to attack spotted spider mines when air units are not available.

Zealots are bigger than marines; don't fit through cracks between flush buildings; are fast with speed upgrade; are good for taking out towers; and should compose the majority of your army. They are good against most any ground unit except for large numbers of Vultures early in the game, in which case you need Dragoons or Cannons for support (Reavers in the later game). They benefit well from attack damage and speed enhancement. Always get speed enhancement as soon as possible if you are fighting with many Zealots. Zealots take out "towers" well.

Dragoons are big and fairly fast moving units - not as fast as speed upgraded Zealots though. They defend well with batteries against several types of units. They tend to fall the fastest against a bunch of Zerglings since they only do half damage to small guys; plus Zerglings have a quick attack rate and can surround the big Dragoon easily. Dragoons are your primary defense against Muta rushes. Besides defending against Mutalisk or Vulture rushes, you shouldn't be building many of these guys early on. They are only for support. Use the gas for Templars or other units. Upgrade their range only if you have many Dragoons.

Reavers are very big and very slow. For best results you need speed upgraded Shuttles to transport them. Distract the enemy Siege Tanks with a couple of Zealots or hallucinations, and then drop the Reaver to let him fire… then quickly pick him back up before the Siege Tanks can fire again. Reavers are very good defenders versus ground units when combined with Zealots. Reavers are especially good versus Hydras, Marines, and Zerglings if supported with Zealots. Use Reavers in pairs for best results. Don't bother upgrading the Reaver capacity unless you are very rich. Have Reavers follow one another to prevent them from firing at enemies when trying to be sneaky or save their Scarabs for later. Scarabs are the ammo of Reavers. Scarabs are the only invulnerable unit in the game. They do massive explosive splash damage. Don't bother upgrading their attack damage until you are wealthy.