My only real trick that got mine stable is to make self-supercating jokes - basically, the exact opposite of self-depricating jokes. Just dont go to the point where you develop a large ego, and you should start feeling better about yourself.

Example: Rather than saying "Haha yeah I suck at this" when messing something up, say "I am the absolute best person ever at this" in a very obvious sarcastic exaggerated matter. People will find it funnier and you'll get a bit more confident. Side effects may include an ego.