Now I bill around $800 per day, but I only work about 6 super-focused hours, and I use the Pomodoro method every day. My clients are happy because I get a lot of work done, and I'm happy because I have to work less.
This is just doing general PHP dev work (Codeigniter and Laravel frameworks), and if I specialized, and if I focused on the ecommerce or finance industry I could probably make more. Most my clients are in the Rocky Mountain West, and so far I have more work than I can finish.
So if you want to increase your earning potential you should:
1. Specialize and master a niche.
2. Network like your business depends on it.
3. Give free seminars and teach everywhere you go.
4. Label yourself as a consultant.
5. Don't be just a programmer. Work with businesses and fix their problems.
6. Know your worth, and don't be afraid to charge what you're worth.
7. Anchor your costs against how much value you'll make your clients.
8. Keep raising your rates until you can't get any work.
9. Work half as much as you used to.
10. And finally, spend time on things that matter like family, learning, and having fun.
Or you can keep competing against bottom-barrel programmers on upwork, and spend the rest of your life working for peanuts. Totally up to you.