TweetIt's hard and if things are still the same, you have to have a degree just to sit for the exam. Things may have changed but that's how it used to be. With that said, NSCA is by far the best cert because it is the toughest to acquire. You have to know your stuff and it's not fill in the blank or multiple choice. There is a practicle section. Their headquaters is here in my home town and I have a buddy who's a CSCS through them. If (when) you get your cert you will be the envy of the other trainers because it's a tough exam.
As far as study, get college books on Anatomy, Kinesiology and Applied Physiology. Don't re-read what you already know. Go to the glossary and look up things you don't know and then study that. The most impoartant will be Kinesiology. If you get that down then you can ace the praticle. That's the most important. For instance, the instructor will do something like a squat and then ask you to explain the movement. What joints are moving, what muscles are moving those joints, what muscles are the stabilizer, etc... An easier example would be if the instructor did a chest fly and asked 'what's the movement?' (horizontal humerous adduction) 'what's the primary?' (pectoralis major) and stuff like that.