Ken Larsen's web site - Tennis
I was a pretty awful tennis player prior to 1990 - not being able to get a serve in unless it was very low velocity. Then, I ordered some instructional VHS tapes featuring Dennis Van der Meer and learned, among other tricks, how to hit a slice serve. That dramatically improved my game, and people no longer shunned having me for a partner.
Besides doubles play, I directed ten round robin tennis tournaments for the local Triangle Sports and Outings Club (TSOC) in the early 1990s. The standard format was that I'd divide the registered players into four teams of equal skill. Then, they'd play against each other round robin style. I would videotape the proceedings, and we'd all adjourn to my house later for pizza and a showing of the tape. A regular named Mort kept everyone in stitches with his flippant observations.