Ok, I am a beginner in magic so this tip may be complete and utter tosh, but don't
over-practice! Yes, I'm aware how silly that sounds, but I used to be very nervous about performing magic. So, I'd keep practicing and practicing until I could perform it with my eyes closed (by the way, this effect was almost self working!), yet I still practiced, and wouldn't perform until I was "ready", but of course I didn't know what ready meant, and I soon realised, when I was asked for a trick and began making my excuses, that I had over practiced, so I just went ahead and did it. It went perfect, as I had practiced to the best of my ability, but I had waited too long. It would, of course, have been perfect if I'd performed it a month earlier!