Becoming a great tennis player can be a lonely endeavour, often times with nobody to practice with. One way to spice up your serving/overhead practice is to utilize the wall (check out the diagram above). Start with gently tapping your smashes against the wall, then graduate to further distances away from the wall.
One tip to keep in mind is to hold the racquet extremely loose. Hit the ball gently, with feel. See if you can hit smash after smash without having to move too much from your original position. Can you control the ball. Rookie players will grip the racquet too tight and just "gun" the overhead with no sense of feel or direction. The best players do not take full cuts at the overheads (sure they can if they want to), but they understand the aspect of placement. This type of hitting against the wall simulates your warmup or match overheads, trying to hit it down into the court (as if you were aiming for inside the service line).