Strategy guides
One standard strategy per matchup, from the why to the build, with what to do when you scout each thing. Written for every level; if you are new, read the first three sections and stop there.
You play Terran
Mech
TvTTerran vs Terran
Siege first, expand behind the line, mine and drop to make them move, and never attack a sieged tank line head-on.
Mech
TvPTerran vs Protoss
Siege-expand, mine the map, keep vultures and tanks streaming from three factories, and take fights only where your tanks are already sieged.
Bio
TvZTerran vs Zerg
Take two bases, build more barracks than feels reasonable, keep marines and medics streaming, and make siege tanks the moment you see lurkers.
You play Zerg
Three-hatch mutalisk
ZvTZerg vs Terran
Three hatcheries and drones, mutalisks to keep the marines home, lurkers to hold your bases, and defilers with plague and swarm to win the late game.
Three-hatch hydralisk
ZvPZerg vs Protoss
Three hatcheries and drones, hydralisks with speed and range to stop the first push, a fourth base behind lurkers, and hive tech before Protoss has its third.
Zergling and mutalisk
ZvZZerg vs Zerg
Match their zerglings, get the spire by 4:00, keep mutalisks alive with scourge behind them, and never let your drone count fall behind without a sunken to justify it.
You play Protoss
Gateway macro into arbiters
PvTProtoss vs Terran
Expand faster than Terran, keep dragoons and zealots streaming from many gateways, see the mines with an observer, and win late with arbiters or carriers.
Forge expand
PvZProtoss vs Zerg
Forge expand behind cannons, corsairs for overlords, +1 speed zealots with templar at 9:00, and the third base behind that attack.
Dragoon and reaver
PvPProtoss vs Protoss
Two gateways of dragoons with range, a robotics facility for the observer and a reaver, then expand and out-gateway them.