I smoke in my room nightly but my room smells fine. What I do, is I smoke in my closet. On top of that, I exhale into a pillowcase. The pillowcase seems to be the thing that contains all the smoke and prevents it from leaving the closet area (thus leaving my room smelling normal).

I also have my laundry hamper right by the door, so if I leave my stinky socks or something right in there, then ppl will most likely smell that instead of any traces of weed. So if you need to hide a smell in a hurry, just leave out something stinky. Or eat some sardines in your room.