StarCraft II: Beating the AI on Hard

Watching others play StarCraft is the best way to learn.  And I have successfully beat the AI on hard using all of the races (1 vs 1).  And the pattern is actually quite simple (on Blizzard's maps at least).

First; we should realize the harvesting is the main bottleneck.  If you have to wait a second to build a unit (unless the game has just started) then something is wrong.

The other bottleneck is production speed.  If you have too many resources and can't spend them on units, something is wrong.

So; here's the overall build order:
1. Get up the 20 units harvesting the mineral fields provided at the beginning.
2. Zerg: get Zerglings (also, build a queen as soon as possible), Terrain: get marines (build two barracks), Protoss: Zealots (build two warp gates).
3. Set up a second base (no air units at this time).  Get 20 units harvesting the second mineral field (while producing a steady stream of offensive units -- your first test is surviving the first wave).
4.  For Zerg start focusing on roaches and move towards hydralisks (air defence) -- if all goes well you have so many minerals to waste that building a third or fourth hatchery for extra unit production is worth-while.  For terrain, build a factory for stronger units, however you should be able to afford 4-5 barracks producing a continual stream of marines.  Similarly, for protoss, 4-5 warp gates can produce plenty of units (but the zealots won't be enough, vary it a bit with them.)
5.  Send waves of units (if there are enough) into enemy territory (scouting may be needed).  I let them die off and focus on preparing the next wave.  If you have the talent, you might want to call back weak units.
6.  Prepare a final wave composed of tougher units (ultralisks, for example).

And victory should follow.  This just rushes the AI with too many units.  It can fail, but it tends to succeed.  If you aren't sure why things went wrong, look at the replays and see how the AI played.