And I'm gonna add that drill classes (a group of 6 or more people with a club pro feeding balls and orchestrating a variety of hitting drills) is NOT the same as practice.
Often in a drill class you will get occasional simple comments from the pro, but no focused direction. I would suggest that you take the money from attending 2-3 drill classes and instead pay for a one-on-one 1 hour lesson with the pro.
Focus on one or two weaknesses, or enhance one or two strengths... but you will learn more in a true lesson than you would in any number of drill classes.
Sure, the drill classes are fun, and there is a social aspect too... but if you really want to improve... drill classes are not the way to go.
That, and as others have said, get a ball machine or find a good wall... and at the minimum- take a bucket of balls to the court and work on your serve.