I prefer to work on a few things at a time for a long time. If a player works on too many things at once, they’ll be mediocre at everything, great at nothing. It’s better to master the most important things first, then start adding in everything else later.
1. Footwork
2. A Weapon
3. 2nd Serve
4. First Volley
5. Mental Skills (could be #1!)
Here is the link to the blog!