This is from the High Times stoner handbook.

Mutes(AKA doob tube, sploof...)
Advantages -
Cheaply made from dryer sheets and a paper towel tube. Effective at the point of usage.
Disadvantages -
They don't work unless you blow the smoke into them. After the first trip around the circle, your forgetful friends will expose this design flaw.

Fans:
Advantages -
Disperse smoke rapidly through air circulation.

Disadvantages -
Unless properly aligned, they can back fire, pushing a fragrant trade wind out the door.

Sprays:
Advantages -
Mask the pot smell nicely.

Disadvantages -
Some paranoid person will invariably grab the can and go apeshit, leaving your room reeking for the next 18 hours.

Incense:
Advantages -
Nice smell.

Disadvantages -
You're not fooling anyone with that incense.

Towel under the door
Advantages -
Keeps smoke from getting out under the door.

Disadvantages -
Relying on the towel alone is like using the rhythm method for birth control. It might work for a while, but roll the dice enough times and you're eventually going to lose.

Ionizer:
Advantages -
Magically clears air with science

Disadvantages -
VERY expensive. If you had that much money for it, you'd just buy more weed anyway.



Also important:
Let the room clear out some before you open the door.
Avoid joints at all cost.


Or, if you want to go REALLY safe, invest in a vaporizer. No smoke, hardly any smell at all, and the little smell that is there smells more like popcorn than weed.