From my 28 years coaching team tennis at the high school level, (in addition to directing and managing tennis clubs and gyms), I'll offer some advice that helped me and my father develop one of the most successful high school tennis teams in the country.
1. DON'T cut! I can't tell you how many kids who didn't SEEM to possess the skills or talent to make the varsity ended up being some of my most prolific and most successful players.
2. Teach your players how to drill each other. There are hundreds of drills that you can do that they work with a partner, (toss and block drills are the most effective.) Teach your players to feed balls the first few days of practice; you can have six to ten players on a court doing various drills
3. You can indeed TEACH a large group of players, (contrary to some of the advice offered here), if you know how.
4. Hopefully, you are going to be around for a few years. If so, then look at the long-term picture: teach advanced stroke progressions; teach advanced strategic patterns; develop drills that efficiently address these two concepts.
5. Obviously, your personality, the way you motivate, etc., will have a lasting effect on your players desire to work hard for you.
6. Use rainy days to improve; where most coaches send players home, we ALWAYS loved rainy days to do several things: a) Use the gym if available to work volleys and footwork drills. (Again, toss and block drills work great in confined places.) Go into the hallways and do these drills; Take the kids into a classroom and watch videos or YOUTUBE clips of players; analyze what the pros are doing, how they are moving, how they set up a point and finish a point. Watch training videos; take tennis magazines and have your players read an article and write a summary; Have them pick a favorite player and have them research the player's strengths, history, and playing style.
7. USE CHALLENGES OFTEN: We challenged at least half our team every day. We had an average of 45 players each team/season with only two coaches; Challenges offer the best pressure situations for kids to learn to fight for their position.
8. Train your kids on how to chart: with large teams, lower kids charted the varsity and JV matches; this helped them actually WATCH the upper kids play with a purpose and the upper kids gained value from the lower kids charting their matches. (Find a charting sheet on google if you don't know how to make one.)
9. Make your LADDER BIG! Make sure every kid can see their position.
10. Create opportunities for kids to play challenges on the weekend or set up practices or mini tournaments for your team. (See if your local adults can come on weekends to play your kids...awesome experience for young kids to play experienced adults. And, the adults usually like to play young kids and then they will like to follow their progress...setting up opportunities to gain some financial support from your community.
11. Read my book, COACHING MASTERY....yes, it is here at Tenniswarehouse. It documents all my coaching concepts that I've accumulated from my 35 years teaching.
Good luck and thank you for helping kids get better!