Here are a few things that have worked for guys I know.
1. There are some good video presentations out there, by some serious names who have won prestigious matches. The thing about a tool like this is that you can take it at your own speed - going over and over a part of it if you need to. At the very least, videos provide a foundation for you to get to learn the concepts, terms, etc. to get started, and to "see how the pros do it".
2. Believe it or not, many guys dry fire - place a target on the wall or in their garage, and (double-checking that their pistol is un-loaded) practicing their draw strokes, presentation, and - for example, if addressing a plate rack - whatever movement(s) they might use to clear the rack. Just the repetition of drawing, slowly but paying attention to detail, and then dry-firing that initial round (use a Snap-Cap) can be very beneficial.
3. If you have the luxury of being able to use the props (door frames, low windows, etc.) that a Defensive Pistol course of fire might use, practice getting into unorthodox firing positions in the most efficient and effective manner. Many ranges will not allow you to shoot from unorthodox positions: prone, kneeling, crouching behind cover, etc.; if you can, fine - if this is not allowed, again, you can at least practice getting into and out of these firing positions in the privacy of your own home (again, with rigorous attention to safety).
4. Practice in front of a video camera. Nothing provides you with instant and valuable feedback like video footage of you doing something inefficient, unsafe, or un-necessary. Even if you just spend 30 minutes drawing and firing double taps, or addressing multiple targets, etc. viewing the footage afterwards can provide you with input you can use to improve.
5. Work with a mentor. Lots of gun clubs have some pretty serious pistoleros who are competitive shooters. Sometimes they are retired, sometimes not. Occasionally you may be able to ask one of them if you could pay them for a few hours of their time one afternoon, where they take a look at what you're doing and offer pointers. Some of them may offer to help you without pay. Either way, having a more experienced shooter help you along can offer you a way to improve rapidly and/or overcome a plateau when you encounter challenges.
6. Join a league or pistol club that offers regular competition, and compete as often as you can. You will learn something every time you step up to the line, if you pay attention.
So these are some ideas that you might find useful.
Focus, keep meticulous range notes, and pay attention to details - e.g. don't be afraid to go slow at first, and you'll find yourself improving sooner than you'd expect!
Regards,
Doc