Uhm... Definitely don't forget to eat something before the meet, I did that once and regretted it horribly!
It always helped me not to watch the other gymnasts at the meet perform, and instead focus on running through my routines in my head.
No idea about the leo, it just sort of happens and you ignore it, haha. A couple of years ago, I had to finish my floor routine with both of my butt cheeks showing because my leo decided to humiliate me! At least everyone watching had a good laugh!