StarCraft/Protoss mission 3: Higher Ground

Establishing the base
Following the pattern developed in the previous campaigns, you are allowed to climb just a little bit further up the tech tree in this mission. Specifically, Stargates are available for warp-in this time around, which means you can build Scouts. Before you start building a victory fleet of Scouts, though, you've got some infrastructure to take care of.

Both Zerg bases (there's one directly to the north of your starting position and one in the left side of the map) will airdrop units on your base fairly often, so build a Forge and work on warping in some Photon Cannons, making sure all sides are protected (this includes the ridge to the north). Then build two Gateways—you'll be pumping out units much faster—to make some Zealots. Now you're pretty much set against enemy attacks. Zealots murder Zerglings, Cannons are good against Hydralisks, and the Scouts that you start with will kill enemy Overlords in just a few volleys of their powerful missiles.

Now you can start working towards a strike force. Build a Cybernetics Core to unlock the Dragoons, and start upgrading as well as making units; ideally, you'll have every available upgrade done when this is over, but for now get Singularity Charge (Dragoon range) at the Core and the Shield upgrade at the Forge.