If your in a small group or on your own in a house and you feel bad, tidy the place up. Shit lying around plays on your mind if your paranoid, or can cause paranoia if your feeling bad anyway (Shit, I'm feeling sick and the house is a mess = panic). Obviously try to avoid trashing the place in the first place.

One thing that I always do now is if your rolling on a table, put a towel or something under it. This will catch anything you drop and if you need to hide it quickly, you don't need to pick up the joint and the hash and the lighter and the cigarette box and the skins and wipe off the tobacco/rocks, you just have to pick up the towel. This got me out of a lot of screw-ups.

Also, anything you don't need soon, put out of view, somewhere no one will look if they were to arrive suddenly.