Cleans are one of the best execises for power and explosiveness. When I do cleans I sometimes press (actually called a push press) at the end of the clean where feet are parallel to each other (that's just my preference). It is different from the jerk whereas when lifting the weight overhead, one does a split postion, then bring the legs together.
For the clean, make sure you don't use your arms to actually lift the weight, i.e., use your arms as "hooks" by keeping your arms straight.
First get the slack out of your arms (keep arms straight as if your going to lift), knees bent, head up, back straight. Now as you lift, use only your legs. The moment you push off, the bar should push away from your legs with just enough clearance to proceed with the lift w/o touching with your knees. As you catch the weight at the shoulders, do a half-squat, then straighten your legs.
Here's a link that may also help.
http://www.exrx.net/WeightExercises/OlympicLifts/Clean.html When the link comes up, right click on the photo, left click on "Refresh page with full quality" and watch the movement.
Good luck.
