If it's white teflon I would probably go about 3 wraps around. That stuff is pretty thin. I would strongly recommend using some pipe dope as well as the teflon tape!
You need to tighten enough so it doesn't leak :P But in all seriousness you just need to snug the fitting on and then go another 3/4 of a turn or so. Just don't crank it on so tight.
You need to use the right size wrench too. If you use a 12" cresent you don't need to put as much force into it as a 8" wrench.