Nate's right. You use 100% of your brain, but how well you use it depends on the person and such.
Arxryl and ziggy, there's no real "right" way to make a psiball, or to do anything in psionics. Basically, it's just like having an opinion, in that almost everyone does it differently. I tend to use
this way, but you should find the way that works the best for you. This doesn't mean that someone "has" your way of doing it, so you should always try different techniques, as well as even small varients in how you do it.