A-B-C. A-Always, B-Be, C-Closing. One of my favorite film quotes of all time (from the screen adaptation of David Mamet's Glengarry Glen Ross) is also my acting/tennis tip for today.
One of the things I love about tennis is that, unlike many sports, there's no such thing as getting a lead and then running out the clock. You must finish every point, and you must win the last point to win the match. In acting, you may not always get to have the last line, but next time you're rehearsing for a scene try playing each line as if it were your last. What does that do to the scene? What does it do to your objective? How does it affect your scene partner? Chances are, it means you'll be pursuing your goal more urgently: to get what you want on your line; or to force your scene partner to give you what you want because of the way you delivered your line - or, in tennis terms, you hit a screaming winner or you force an error from your opponent with your shot. In both acting and tennis, it's about playing with urgency. Nothing should be casual. Nothing should be without specific purpose. Otherwise, you're playing recreational tennis - which can be fine - but it's not what people pay to see on Broadway or at Wimbledon. Watching guys like Federer and Nadal each trying to get the last word in against each other - seeing them constantly trying to top each other with each stroke like two characters in a David Mamet play - was one of the things that really got me thinking about the parallels between acting and tennis and the inherent drama that comes with both when done right.
Conflict drives a play - and a tennis match. One of the students who I coach said to me when we first met that she felt her main strength as a tennis player was her ability to keep a rally going. I knew what she meant (and consistency is, of course, very important) but I told her - for the purposes of match play - to work on being good at ending rallies. Likewise, in acting, don't worry about if or how your scene partner responds. Get what you want. That's your job. That's your worry. It is not your job to make life easier for your scene partner anymore than it's your job to keep a rally going during a competitive tennis match. End the point. Get what you want. And always be closing.