Tennis racquets have different grip sizes and I am not sure which one would be the best for me. Is there an easy way to find this out?
There are two rules of thumb to determine your correct tennis racket grip size:
Hold the racket by the handle as you would while playing and see if you can insert your your non-dominant index finger in the space between your palm and ring finger tip. If your index finger is snug, the grip is sized correctly.
A player can measure his or her grip size with a ruler. Measure the distance from the tip of your ringer, down to the horizontal crease in your palm, closest to your wrist.
These methods are described in greater detail with photographs here: http://www.tennis-warehouse.com/LC/Gripsize.html