Do a firm, loud (but not yelling) 'No' to stop the behavior. Then I redirect with what the positive of the action would be. If it's an accident, I take the pup outside, and clean up the mess. After it's clean he/she can come back in. If it's chewing on something they aren't allowed; I move the pup and offer something appropriate to chew on.
If it's ruff playful biting then I yelp, act hurt and refuse to play with the pup. . .
I don't do timeouts; you're only supposed to keep a child in time-out for 1 minute of every year of life. Even then they don't really comprehend time-outs till they are a couple years old. I just don't really think the doggie can get/understand the full benefits of a time-out more than a couple minutes long. So anyway, that's why I use redirect instead of time-outs.
