Many players, when serving, either serve with a weak motion and get very little spin, or use a somewhat fast motion, and get only a decent amount of spin. However, if you want to get real spin on the ball, you have to think of the serve as a "violent" motion.
Think of it this way. If you want the ball to spin at 100mph, you need to get your racket moving at 100mph. You can’t do that by pitter-pattering around – you have to really stroke it – and that means getting "violent." After a good session practicing your serve, you should be sweating from the effort.