So my season just started, and I'm finding that while a lot of my opponents are having difficulty returning my serve, my form drops off heavily after about 1 set given that it goes back and forth some. I suspect that alot of it has to do with a decent amount of my service games going to duece. My serve speed is about 90 for 1st and 60 for second and my consistency is about 50-60 for 1st and 70-80 for second. I want to be able to keep these kinds of numbers for an entire match and even improve my second serve. I know my consistency can go up with practice and my endurance is pretty good, but I want to know some drills or tips for preventing my form from degrading on the back end of matches. My mental strength is improving but I also need to focus on regulating my breathing during matches better.