Check Your Door First
With the door closed, pull the emergency release cord and lift the door to see if it opens and closes smoothly. If it doesn't, the problem is with your tracks, rollers or springs rather than your opener. Learn more about garage door tune-ups.
Play it Safe
Unplug the opener. That way, you won't lose a finger if your unsuspecting housemate hits the remote button while you're working. Even worse, you could electrocute yourself, in which case you wouldn't be able to blame your housemate at all.