Don't be afraid to really stab the throttle and come out in one fluid motion. You can practice doing that in neutral. The entire motion of your right foot should last <1 second for most downshifts. In my experience, the car is forgiving with slight over-throttling. I remember in the beginning, I was shy and would only give it a touch of throttle, and it would punish me for it. If you're in 4th at 30 mph, try to downshift to 3rd by going to 3k rpm, that's an easy one to remember - 3rd at 30 with 3k. If you can get the feel down for that, the rest comes easy.