Tip #1: Where a jacket/sweatshirt or anything else that you can remove. Change shirts if you want...

Tip #2: Smoke a cigarette to cover the smell if possible. If you don't smoke, or you're too young to be smoking (don't admit that here though), use cologne or something. As a smoker, NOBODY will ask you why you smell like smoke, but parents are quick to ask why you smell like a whore.

Tip #3: Use a pipe or bong if possible. Joints and blunts tend to put the smell on you a lot more than pipes/bongs. Not sure why, but with a pipe the only thing that will smell like weed is the hand that you light the bowl with.

Tip #4: Smoke outside, and then stay outside for a while. After 10 minutes or so you won't smell like weed at all...