Well, my mom doesn't care that I smoke cigarettes and cannabis in my room, so I'm lucky as far as that goes, but, I have some advice, on what you can do to prevent this from happening in the future.

1. Trash your room. That way, when your mom wants to search, she won't even be able to walk on the floor, let alone find ANYTHING
2. Hide your stuff where she would never look. Even in a different room. If she's searching for your stash, I doubt she'd check underneath HER matress, or in your cd player, etc... you get the idea)
3. If you want to smoke in your room, keep a fan going, and the window open, or buy a gas mask filter, or something similar, and exhale into that.

Hope I helped.