I am speaking from experience. I have been asked to join a relatively well known company as an instructor. Though I'm just starting out doing this for money, the road I took started with the NRA courses.
As stated, get NRA certified. This will open doors (insurance companies love the NRA courses).
Since you mentioned CCW and personal defense courses, this implies handguns. Attend *many* gun classes with a variety of gun trainers. Variety is the key; learn *every* technique possible, even if you think it's bull****. Become an expert in sighted and threat focused fire. However, it's also very important to focus on the fundamentals--the basics are so important, that you could specialize in trigger pull and still have work (look at some of Bruce Gray's material).
The most important actions you can take are: 1) take notes during class and practice what you learn AFTER the class, 2) teach others basic shooting techniques, and 3) teach others what you learned in class. I cannot overemphasize the teaching part: you should be instructing people around you. Even if it's just a minor correction or an hour. Develop the ability to diagnose problems by watching the shooter.
However, to get there, you need to be good. This takes time and burned powder. Get a 22 caliber rifle, pistol, and revolver and SHOOT frequently. Airsoft can really help with this, but you still need to shoot real bullets. You MUST be able to perform, on demand, all firearm manipulations and associated movements. You should shoot every week and dry fire at least twice a week (if you're watching TV, you're dry firing, loading, moving, etc). If you specialize in some sort of competition shooting, then you need to compete. Over the course of your training, you will learn how to practice perfectly. Take this to heart and be able to teach it to others. A 16 hour course will mean nothing in 6 months if the students never practice or practice badly.
You will also need to know the course material and some law. Various states offer instructor programs through which certification is granted. You will need to know this material perfectly. Networking will help in this area; perhaps you can get a lawyer or police officer to assist in teaching the class (it may be required by the state).
Finally, it's difficult to make a living as a full time trainer. Get used to travel, because very few have the luxury of a facility like Gunsite. Customers are difficult to find and expenses are high. Insurance is a bitch, and then there are the costs of sundries, travel, food, and so forth.
Good luck! If you find the road to get there pleasurable, hopefully you'll find the work rewarding.
