I admit, this is how I have been when I was a beginner in magic. After learning a trick, I practice a little then perform it almost immediately. It was okay at first but after learning the more complicated tricks, I find myself struggling in performing and end up "flashing" a couple of times. It wasn't really a big problem back then but as time went by, I had tougher audiences and this was not helpful at all in performing. It has affected my confidence as a magician and it results to a mental block. This problem is obviously not only my problem, but a problem of magicians as well. I've seen a lot of magicians performing (actually murdering) a very good trick.
This is why now before performing any trick for audiences, I practice it everyday and if I think I am ready, I perform it in front of my family and my friends. If the trick goes well then I will perform it one more time to the toughest audience there is in my magic, who is no other than my girlfriend who sees if I'm doing it well. Her silence is good enough but when she laughs then I know that the trick has gone good.
So have someone who could provide you the proper critique when performing. It may be a magician, but I prefer a non-magician because after all, the one you would be performing for most of the time is a non-magician.