I'm actually one of the most expensive trainers in Toronto, and here's how I did it:

1. I wrote 5 books.
2. I promoted the heck out of those books, from Amazon, to book signings in stores, etc.
3. I was able to get my own radio show. To this day, radio shows have way more clout than podcasts. People know that anyone can start a podcast, but it's the perception that only a special person can be a radio show host.
4. Be able to communicate complex concepts very clearly.
5. Point out common mistakes in your competitors, without calling them out by name.
6. Do public speaking
7. Create an email list.
8. I appeared on TV multiple times (and it's not as hard to get on there as you think).
9. I appeared in local newspapers a number of times (also not as hard as you think).
10. I got the mayor to endorse my books.
11. I made sure everyone knew about the above.

Oh, and on the technical side of things: I took a ton of courses, and spent tens of thousands of dollars studying about exercise, nutrition, hormones, neurology, etc. The centerpiece of good marketing is a good product.

Look at it this way: if you have space for only 10 clients, 2-3 times per week, but there are 50 people who want to work with you, you can raise your rate so that only the top 10 are able to work with you. That's what it really boils down to - creating demand.

And the way you create demand is by first being good at your craft, second, making sure that everyone knows how good you are, and third, creating the "aura" of a celebrity.