If you are playing in a tennis tournament, then you would need a good level of aerobic fitness to last the day and still have energy for the last game. Work on it by doing one of the above mentioned activities at least 3 times every week for at least 20 minutes each session of aerobic exercise. A structured programme will give you more benefits. Obtain advice from people who are experienced in exercise. If you can get to a gym, using their cycles, rowers or steppers are all aerobic exercises along with the classes, both circuit and aerobic.
Muscular conditioning is done through exercises against resistance.
This can make you tennis serves and strokes more powerful, and assist in other ways like injury prevention. Try to do some exercise every day. Any activity is better than no activity. Playing games other than tennis can allow you to get fitter without putting the same stress on your body the same way as playing tennis all the time. Doing some light exercise helps the body recover from your exercise and may reduce injuries.