Advertise to train other people's horses and give lessons. Usually the rider needs training along with the horse.
I do not recommend training your own horse. I've had bad luck. I did pre-purchase exams on both my horses. They both passed. And they are both lame. I bought my mare directly from the breeder. Looked at her, looked at her parents. Thought she would be perfect. She was 2 yrs old and not started. Nice straight legs. A few months after I started her under saddle, I noticed she was not quite right. Whatever it is does not show on X rays (normal). I've had 2 vets look at her and they have no idea. Last vet said take her to the university for a nuclear scan which is an additional $1000 or more.
My horse before that had navicular syndrome. X rays did not show any changes... It turned out to be soft tissue damage. She than went on to develop degenerative ligaments (most horses with it appear healthy, but it can strike at any age, and you can't test for it).
So even if I had done a pre-purchase with X rays all the way up both horses would have passed!
What is your plan for dealing with an incurable lame horse? Are you willing to put it down? Give it away for free and hope it doesn't end up with the meat buyer? Keep it and retire it?
What happens if you get hurt while training (bucked off and break a bone)?
It is better to train for other people. At least than you don't have to worry if the horse goes lame. You don't have to worry about board and feed costs.