I have the same problem. I think to much while shooting or whatever, it makes me nervous, once I get nervous I doubt my shot, after I doubt my shot I have already missed it.What I do? I work on making myself numb. I watch video clips of big time clutch players like MJ and whoever else. I watch them make the clutch shots. I read about them talking about making the clutch shots. Then I practice adapting that to fitting my needs.It is the hardest thing, but it is the truth. You have to clear your mind. You have to let yourself play the game sub consciously.I know you most likely want a real way to practice this. The truth is- there isn't a real way besides getting actual expierence. Although, there is one thing that can help to a degree, but it isn't fun and you have to be committed to getting better. This is how it works:While you are practicing your game, setup some "in game situations" in your drive-way, or where ever you might play. Example, make a cross-over past a chair or something and then do a pull up jumper. The stakes? You set something up before you take the shot. Think of something you enjoy doing, something you do every day, something you like. Put that on the line. Whether it is no TV for a week, you don't get to eat something you like, you make yourself do something you don't like to do, you do sprints, ask out a girl you think is hott, or whatever. Set the stakes up before you begin the shot. Do this as many times as you want or do it to end your own practices. The only way this will work is if you follow through with whatever you bet on after you miss the shot. If you have to, get your friends to help you follow through or whoever will keep you honest.What does this little drill do? Depending on what stakes you setup and if you actually follow through with them on a miss, this drill will help you get used to shots under pressure. Is it fool proof? No, but you asked for some way to help right?
