Let's add a few more:

• Never bitch about someone else’s weed being no good. If you don’t like it don’t smoke it!
• Thou shall not turn down a smoke. Ever! Conditions permitting!
• If smoking from a joint, never put the whole thing in your mouth and get it all sopping wet. It is disgusting and it messes up the joint.

EDIT: 2nd Bullet, not to be taken literally, obviously if you have a math class in a half hour you shouldn't be smoking.