Get used to being bruised. I used to play all the time in college and while it's a FUN game to play you're going to get welts from the ball and bruises from diving on the floor all the time.
The thing that helped me most from a mechanics standpoint when I used to play was mastering that backhand shot. In tennis when you want to make a powerful backhand shot you sometimes have the time (and no fear of wall collision) to take a two-handed backhand shot to give it extra velocity and top spin. When you're going for soft touch and/or back spin you can always one-hand it. In racquetball you don't have nearly enough time to hit a powerful backhand shot most of the time (plus you can't two hand it like you might in tennis) so you have to master hitting that backhand with power on quick turnaround time.
Another thing is to just spend time practicing how to return serves. The drive serves never bothered me NEAR as much as somebody who could lob serve well (i.e., pin you in the back corner where you have to return a weaker richochet shot.) I was never able to get the hang of those (particularly when I was forced into playing a backhand, richochet return) and always lost positioning for the remainder of that point.