Head Size
The head size of a racquet is a huge thing to take into account when making your decision. Power is directly related to head size; a larger head will give more power than a smaller head - assuming all other factors are equal, so this should definitely be taken into account. A larger head will also provide a larger sweetspot and be more forgiving to off-center hits. Most tennis racquets today offer heads in the range of 85 to 135 square inches, with the most common being 95-110. As a generalization, more advanced players prefer smaller heads for more control, while beginning players prefer a larger head for its larger sweet spot and enhanced power.
Length
Tennis racquets are available in lengths from 27-29 inches, which is the legal limit for tournament play. A standard racquet is 27 inches long, however, a longer racquet will provide more reach on groundstrokes, added height on serves, and slightly more power in general. As racquet lengths increase, the total weight actually goes down, to keep the balance of the racquet correct.
Weight and Balance
The weight and balance of a tennis racquet is by far one of its most important characteristics. Most pros use heaver, head-weighted racquets, because it gives the most control, assuming the player can create their own power. These racquets usually weigh 11-13 ounces.
Another option is a lightwieght head-heavy racquet. A few years ago, Wilson developed a way to remove the weight from the handle of a racquet and retain the balance and heavy-head. The racquet design, which was used in their Hammer and Sledge series, was lighter overall, while still retaining mass in the upper hoop, where ball contact occurs. Several other manufacturers have now picked up on this design.
The advantage of a lightweight head-heavy racquet is increased maneuverability without sacrificing power, especially on groundstrokes. Some players complain that these racquets feel "light" and transfer more shock to the elbow and arm, however, it is mostly based on preference.
So, in summary, when shopping for your new tennis racquet, some of the most important things to investigate are head size, length, and weight and balance. Also, remember that no matter how good a racquet looks on paper, there is absolutely no substitute for demo'ing the racquet and seeing how it feels during actual play.
