I see many tennis players standing straight up and with their feet close together when standing in the ready position. Try keeping your feet at least shoulders width apart and knees bent. This will give you a much better chance of reacting quickly to your opponent's shot. A wide stance improves your balance and allows you to explode in the direction of the ball.
Starting with your knees bent will allow you to push off by straightening your legs and will give you a good, quick start to your next shot. This will also help you when recovering after your shot. Also, it is much easier to start low and adjust your position up (if the ball is high), rather than being up high and having to get down very low, if the ball is in front of you or if it stays very low. The low position also gets your line of vision closer to the height of the ball as it is bouncing and allows you to see the ball better.
Try over exaggerating this position and you will benefit from the improved balance and explosiveness it provides. You will end up running down more balls and positioning yourself better at the point of contact, making it a difficult day for your opponent.
Steve Annacone, USPTA Elite Pro, is the Director of Annacone Tennis, www.annaconetennis.com and MyHamptonsPro, www.myhamptonspro.com in East Hampton, NY . Steve is also a tennis professional at Ventana Golf and Country Club in Tucson, AZ. In addition, Steve and Miguel Coelho have introduced the JET (Junior Elite Tennis) program at the Tucson Jewish Community Center for high level players ages 8-18. Please contact Steve at email@example.com