There are a huge number of resources available to help you learn more about playing racquetball. Books, videos, and trainers that can work with you via digitally videoed sessions are all possibilities. Local instruction would be my first recommendation though. Nothing compares to the live feedback of someone that knows what they are doing and what to look for, right there in the moment.

Videos – Online
Racquetball Warehouse had four amazingly strong series of instructional material from very different coaches. Unfortunately, when they left the racquetball market, they deleted their YouTube channel, and all of those videos were lost.

Inside the 209 has 20-30 minute videos that feature great players and coaches from Stockton, California.
RacquetWorld produced a set of videos with Jim Winterton and a new series with Rocky Carson.
Pacific Sports Warehouse has a series of videos with Aaron Embry.
Royster Racquetball produced some videos with Cliff Swain.
RacquetballTim does a great job examining game play and making recommendations to improve the game of those being critiqued.
The Racquetball Practice Program put out some videos explaining good ways to practice shots.
Coach Antonio put out some off court racquetball exercise recommendations.

Books
Championship Racquetball by Fran Davis and Jason Mannino (on Amazon)
Winning Racquetball by Ed Turner and Woody Clause (on Amazon)
Advanced Racquetball by Steve Bo Keeley (on Amazon)

or in Spanish: Raquetbol De Novato a Profesional by Aaron Palomino

There are lots of others to read if you want alternate viewpoints. Search on Amazon.

I am an Amazon affiliate. I will earn a commission on the books linked above or the DVDs linked below, if you make a purchase, at no additional cost to you.

Videos – DVD
Building Your Racquetball Dream House – by Fran Davis, featuring Jason Mannino and Sudsy Monchik
Beginning Racquetball: Skills and Drills by Jim Winterton
Advanced Racquetball Secrets of the Pros! by Jim Winterton
Secrets of Power Racquetball: Mastering the Basics by Marty Hogan
Secrets of Power Racquetball: Tips for Advanced Players by Marty Hogan
Play Better Racquetball: Skills and Drills by Shane Vanderson
Play Better Racquetball: Strategies by Shane Vanderson

Udemy has 6 of the 7 DVDs listed above available as “courses” for ~$20 each. If you don’t have a DVD player close to your racquetball court, this might be the way to get your practice to be a bit more effective.
https://www.udemy.com/courses/search/?src=ukw&q=racquetball

Professional Coaches and Professional Players that coach
Cliff Swain
Fran Davis
Jim Winterton
Sudsy Monchik
Manilla Athletics
Key Racquetball