for me it's the poly strings that did me in and playing too much. wrist curls, extensions etc. and an tennis elbow strap helped even though it took some getting used to
Depending on your level of play many things can contribute to tennis elbow. Racquets that are too stiff if you are a intermediate player, but mostly your form,(swing etc) Try using softer strings like multifiliment and stay away from strings with Kevlar, polyester and such. Even playing with less tension should help. I have a sure fire way of getting rid of tennis elbow. I have told several people and they all said it worked. Contact me at www.racquetattack.com or email me at racquet_attack@yahoo.ca and I will send you the info.