Starcraft – Why does Zerg AI get stuck

There are so many different build orders to use against each race it's ridiculous. Also consider that good players will be able to shift their build to better react to their opponents.

That being said, I think the most common one is some variation of a 9 pool build.

* 9 - Spawning Pool
* 8 - Drone
* 9 - Extractor
* 8 - Drone
* 9 - Cancel Extractor
* 10 - Overlord
* @100% Spawning Pool - 6 Zerglings 

I should warn you that I am no SC expert player, or anything. I get most of my info from http://wiki.teamliquid.net/starcraft/Strategy_%28Zerg%29

Knowing build orders, knowing when to use a build order and knowing when to change your build order on the fly are all very complicated questions with very complicated answers. If I were you, though, I would start with the 9 pool. Learn it's advantages and weaknesses over other builds. Also you should think about what the build is capable of, what you are able to tech into from this build and etc.

If you see your opponent expanding, you know it's safe to expand. He's spending minerals to expand, which will delay his attack and give you time to get up defenses for your expansion if necessary.

If you see the makings of an aggressive build (early spawning pool or multiple barracks/gateways), you may want to hold back on your expansion until you see exactly what he's doing. A fast attack will beat a fast expand every time.

If you see your opponent building to turtle, then expanding is your best option. He will be stuck in his base and is essentially giving you free reign over the rest of the map. The best way to defeat a turtler is through macro.