If you want to compete in USPSA, take a class. Seriously, it's difficult to improve if you don't know what you're doing. Below are my classifier scores for 2014 and 2015. In 2014 I went to a bunch of classifier matches with the hope that I would progress. I didn't. In 2015, I took a class in February and shot matches with only one classifier stage, you can see the improvement in my scores and consistency.
A class can teach you how to practice, what to look for, and how to improve. Even if you're just an occasional competitor, taking a class will make the experience more satisfying. There are plenty of great instructors out there to help get you started, so go do it.