Sorry for the lack of pictures I'll add more in about a week.
Step 1: Materials
2. Two or more tennis rackets
5. Common sense
Step 2: Location
Step 3: Soaking the Ball
When tennis balls are made, they're filled with compressed air. this means that the first time a ball is used for flaming tennis, you must use only a little gas. If you don't, the compressed air will exit the ball on the first few bounces, resulting in a spectacular pyrotecnics display, but sadly not the result we want. Using a small amount of gas, the ball will still flare up, but it wont go out or waste your gas, meaning you can play longer, and have more gas left over.
Step 4: Lighting and Serving
Lighting is easy, simply place the soaked ball on the ground and use a lighter to catch it on fire.
To serve, simply place the racket on the ground near the ball and using a scooping motion, launch the ball.
Step 5: Rules
1. Keep the ball off of grass and away from flammable materials/objects.
2. Don't hog the ball.
3. Tennis rules optional
4. Have fun!