Books are interesting, but this is not really the sort of thing you really learn well from books. I don't think there's any good substitute for hands-on training.
I'm a big proponent of good professional training. Among other things, there is really no good substitute for a qualified instructor watching what you are doing and coaching you based on what he sees. Remember that practice doesn't make perfect. Only perfect practice makes perfect.
Practice also makes permanent. If you keep practicing doing something wrong, you will become an expert at doing it wrong. So some good training shows you what to practice and how to practice it. It thus helps you avoid bad habits which later on can be an awful hassle to try to correct. (And a good way to regularly practice some of he basic skills is IDPA and/or USPSA competition.)
If there's an NRA certified instructor in your area offering NRA Personal Protection Inside the Home and Personal Protection Outside the Home classes, taking both classes would be a great way to start. They will give you a good grounding in practical marksmanship and gun handling, and they will be a good foundation if you decide you want to go even further. They also go into legal issues around the use of force and both mindset and tactics.
Competently keeping or carrying a gun for self defense involves more than just marksmanship.
 You will want to know and understand the legal issues -- when the use of lethal force would be legally justified, when it would not be, and how to tell the difference. You will want to understand how to handle the legal aftermath of a violent encounter and how to articulate why, in a particular situation, you decided to take whatever action you did.
 You will want to know about levels of alertness and mental preparedness to take action. You will want to understand how to assess situations and make difficult decisions quickly under stress. You will want to know about the various stress induced physiological and psychological effects that you might face during and after a violent encounter.
 You will want to develop good practical proficiency with your gun. That includes practical marksmanship, i. e., being able to deploy your gun and get good hits quickly at various distances. It also includes skills such as moving and shooting, use of cover and concealment, reloading quickly, clearing malfunctions, and moving safely with a loaded gun.
The NRA Personal Protection classes only scratch the surface, but they at least touch on these subjects and get you started on the right track. From there, you can go as far as you'd like.
Personally, I take classes on a regular basis (most recently, just shy of a year ago, the Intermediate Handgun class at Gunsite in Arizona). I practice regularly, both dry fire and live fire drills. I practice presenting my gun from the holster and engaging targets at various distances. I practice from about 5 yards out to 25 yards. Practice close in tends to involve drawing and quick shot strings. And although most defensive encounters are close range events, I practice at longer distances as well. Shooting at longer distances helps develop and maintain basic marksmanship skills, especially trigger control.
Is all this really necessary? That will be up to you to decide for yourself. It will depend on your personal view of what you need to be able to do to believe yourself to be competent. But --
- If we wind up in a violent confrontation, we can't know ahead of time what will happen and how it will happen. And thus we can't know ahead of time what we will need to be able to do to solve our problem.
- If we find ourselves in a violent confrontation, we will respond with whatever skills we have available at the time. If all you know how to do is stand there and shoot, that will probably be what you'll do. It might be good enough, or it might not be.
- The more we can do, and the better we can do it, the more likely we'll be to be able to respond appropriately and effectively. The more we can do, and the better we can do it, the luckier we'll be.