I'll add a "Do" to the list- if you mess up, make it look like you did it on purpose.
At this weekend's con, I did a dance with lightsabers, and those grips got kind of slippery when my hands started to sweat. I ended up dropping one of them a few seconds before the end of the routine, but I didn't let it stop me, I performed one last flourish and saluted with the remaining saber as my music ended, and the end result was that most of the audience didn't notice! Those who did said that they didn't hold it against me, what mattered was I didn't let myself get flustered, and I kept on going.
Likewise, a Catwoman cosplayer at the same show fell on her butt doing a move, but she got right up and kept going pretty much as if nothing had happened. The audience forgave her too.