I use sleeping pills the night before. Other things that will help you sleep are to stretch before sleeping, and to relax your mind and allow your thoughts to sort of float instead of focusing on a particular fact (especially the upcoming fight). I like to close my eyes and mentally draw images of planets or something else vague, puts me right to sleep.
I also take caffeine before fights. This gets me excited and helps me turn nervous energy into focus. But this may or may not work for you.
A lot of fighters also build focus by doing visualization shortly before the fight: visualizing confidently climbing into the ring/octagon, the referee starting the fight, yourself perfectly executing your gameplan, and then the referee holding your hand up in victory at the end of the fight.
It is very helpful, in my experience, to have a trainer with you before the fight warming up your standup, ground, sprawl, clinch, etc. skills so that you will feel as if each element of your game is warmed up and ready to be used. You can also take that opportunity to discuss your gameplan with him; verbalizing it will build mental confidence in that plan. Your partner should also be encouraging you the entire time, boosting your confidence level.
