For excellent references on strecthing and training muscles, check out the FAQ's in rec.dance and rec.fitness. Training programs for competitive skaters are very rigorous. In preparation for competitions the skater must improve their anaerobic endurance, since the skater's heart rate is way above what they could maintain for any length of time. For the rest of us, aerobics classes are a good bet. Find one with lots of floor work and stretching.
Stair climbing is excellent.
Try taking them two at a time. A ballet class can be very helpful. 8.1 weight training Weight training is also good, especially for improving jumps. In skill sports, such as skating, there is controversy over weight training. This supposedly will prevent psychological and neuromuscular confusion over whether you're performing the desired skill, or the weight activity that's like it.