You can improve either way? Play less or play more. Many players believe that if they play more, they will get better. For years I taught my students to hit more balls and stay on the court longer. Long ago I discovered that this often leads to "burn-out," over use injuries and boredom. Many of these players attack their goals in the short term, however they do not continue playing into adulthood, usually from burnout. I believe hitting thousands of balls mindlessly causes this.
 
I have found that many of my highest ranked junior players have quit playing as adults. My new approach is different. I make sure my students have fun. I make sure they have great form. Then, I teach them to play hard, to win and to have fun. Never worry about losing. You will not win all the time, but you will have fun trying to win. I teach them to "go for their shots" -- "pull the trigger on their shots." Focus 100% while on the court, have fun, go home and enjoy the day.
 
I find this approach allows players to play into old age, having fun with fewer injuries and no burnout. This is where more is not always better. Tennis is a sport for life, enjoyment, exercise and a social event.
 
Good luck on the Court!