Start gently, both in intensity and frequency. Get used to warming up and stretching at every session (if it's a fundamental discipline for every serious athlete and sportsman, maybe it should be for you, too.) If you're starting something new, start slow and steady. Give your body a chance to get used to it, and to build up the strength and stamina and flexibility that you're going to need. If you're aiming for three to four sessions a week, build up gradually.