Jumping rope can be a good aerobic exercise. For most people it´s pretty vigorous, so intervals may be the best way to go. Warm up with some brisk walking, then jump for two minutes, rest a minute or so, jump two, etc. If you can go longer, do it. Add half a minute to your jumping and/or shorten your rest periods if you want to improve your jumping time and make this one of your main exercises. Make sure to choose a surface that isn't too hard. Like other cardio exercises, work at a pace where you´re breathing a little hard but can still talk.