Assuming you want to become an NRA Certified instructor, go to
http://www.nrainstructors.org/searchcourse.aspx and click on the type of course you want, e.g., pistol, rifle, shotgun, etc. The website will show all of the Instructor Training courses of your chosen type within the radius of the zipcode you enter.
The Instructor course (Basic Instructor Training or BIT) takes up most of the first day, and the 2nd day is oriented toward the specific firearm type. Once you have completed BIT for your first firearm type, you only need the 2nd day of any other type (which lowers the cost of add-on certifications).
You should have a liability policy in case one of your students (or you) do something boneheaded that causes injury. NRA offers a Liability Insurance policy that provides good coverage. Mine costs $300 per year.
You should consider forming an LLC and run your courses as a business, noting income and expenses on a Schedule C at tax time.
You can use the same NRA Instructor website to find out who else is offering the course you want to teach and how much they are charging. The BIT module includes a chapter on how to gauge what you should charge in order to break-even or profit. The state plays no role, so far as I know, in what you can charge your students.
Importantly, you will need to create a relationship with a range where your students can complete the live-fire portion of any shooting course. Many ranges will not give "outside" instructors access to their range for your students because they feel it takes revenue away from the instructors that work for the range directly.
Good luck as you pursue this vocation. I have found it highly rewarding.
