I suspect it is a tough business. I'm not a life coach (but am a mental health professional) who happens to offer consulting. There is a slice of people who are motivated to learn and get better, but also open to wanting assistance (as opposed to bootstrapping everything and just learning it on their own (whether they are successful or not).
I think a huge challenge is that people will want to know that you can solve their specific problem(s). My guess is that the easiest way to market your services would be to pick a niche and focus there. Share some results, get some testimonials, and show prospective clients that you really understand their business/field. For example, if I recently opened my own dental practice and want help with marketing my services I'm going to want to know that you at least have expertise in marketing (perhaps you've helped someone create a social media campaign, etc.) and it would be a bonus if you have an understanding of the challenges of a new medical-related business.
Most life coaches (websites that I've seen) focus more on general coaching, motivation, time-management, and mindset stuff. I'm not saying that is unimportant. But it is so much easier to find clients when you can say, "I solve X & Y. If your problem is X and/or Y, then I know I can solve it and make you more money and/or save you time."