Here's a simple drill you can shoot on the range or during a dry fire session. The Focus on Four Shooting Drill is great for warming up, and it can help you improve both your shot transition times and your reloads!
To shoot the drill, from the holster or low ready, draw and Fire:
String 1: Two shots on 1 through 4
String 2: One shot on 1 through 4, reload then one shot on 1 through 4