I used to curl my pinky on my picking hand under the strings while playing fast rhythms, sometimes it still happens but i notice and change it.
I think my biggest mistake was trying to string up a guitar witha floyd with the balls still on (first time ever restringing a guitar) i kept trying for about 10 mins then looked up on the internet how to do it.
Another thing i used to do that was bad was take tone advice from people on the metallica forum.... actually that is probably my worst mistake.