I started playing tennis again six weeks ago. It's been a lot of fun to play and explore how I can get better.
In the first match, what stood out was how I had a lot of anxiety and performed very poorly. Since then my biggest focus has been on developing my attention.
I follow a simple approach:
During points, I watch the ball. I come back to this, repeat it, a bit like a mantra. I try to go into every point, with the reminder to "Watch the ball closely."
Between points I focus on breathing through the nose.
This has helped me a lot. It is a much better object of attention than to worry about the score or if I am playing well or not. And in the process of practicing this, I have been able to relax more.