Don't die.

Honestly, it's been a long time since I played and I never really played that seriously back in the day. I'd say don't forget to expand, and build more hatcheries when you can. Being limited in how many units you can build based on the number of larva you have is a bit rough, so once your economy is rolling make sure you can keep that production up.

Also, I don't know if it still works, but apparently sticking 11 mutas and an overlord in a control group makes them stack even closer than usual and attack all at once. To say that this is would be very effective if it still works is a bit of an understatement.

I used to play a lot of Zerg actually, and with a friend of mine worked out a build for getting some very fast mutas out. Usually so fast that your average player had trouble doing anything. But that was a long time ago now. Oddly enough, I'll probably be playing Protoss come game day.