...? 12hatch 9pool... so, you make hatch at 12, then kill 2 drones, then make pool? lol oO
12hatch 11pool zvt is your best bet. Also, stop playing comps, it hurts you. You'd be better off watching pro reps and getting raped by humans until you get better. Also, that force is no rush. If you don't have time to prepare for it even though you know it's coming then you have some serious speed issues. Make sure you mke your ovys in time, a little before you need them, so that there's no delay.
Well, first of all, I don`t think this should be in the main forum; it has not much to do with mapping or this page. But who cares ;)
So, I guess you are more of the "noob" type player ;) I consider myself average, and I have no problems against 3+ comps at once...
Against computers (predictable...), I suggest to always go for 12 hatch at natural. Now usually you would add an 11 pool to that, but against a comp you don't have to. 14-15 pool is just fine, you actually can squeeze a 15 hatch inbetween. Make sure you harvest with one drone per mineral patch, so slide some drones from your main to your natural.
Start making creep colonies, at your natural of course. Preferrably in a straight line in front of your hatchery. 5 of these should be enough to hold any terran computer.
Make 1 pair of lings, save the money for drones. Put one ling in front of your opponents base. When you see him coming out, morph your creeps into sunkens. Also make about 6 zerglings, just in case.
Then pump either muta/ling or hydra/ling/lurk and kill that terran...
Now for the "real" matches, against humans: There are lots of variations to zerg build orders; zerg usually adapts to the opponents actions. In general, you should try to get as many drones/expoes as possible early on (requires good scouting), and when you feel that you can do it, you should switch to mass unit production.
In the mean time, you can harrass with muta, lurks and drops (pretty rare nowadays, but a hydra/lurk drop still can be devastating if done correctly).
I can only give you this very rough guidelines, as zerg bos rely heavily on your opponents actions. I also suggest to watch pro replays, with vision of only one player and examine why, what and when he did something.