While serving tennis balls, I felt strain on my forefinger and wrist. I diagnosed that I was manipulating the racket with my hand and fingers. I relaxed my hand and fingers letting just my elbow and shoulder bring the racket into the overhead loop. Once that became familiar I felt less like a beginner. I think beginners move more with their hands, so they get less power and maybe injure themselves more.
Now if I can remember what that feels like and execute the next time out, I’ll believe I’m improving.