Agree with everyone else on creating a Facebook page and branded t-shirts. We also had great success with a sandwich board sign that we put up whenever we did workouts.
Creating a profile on SweatGuru.com is another great (free) way to get discovered.
Offering to do a free demo to local businesses can also help drum up some new clients. You could try giving them a discount for signing up after your demo.
Do you have a Facebook page set up? That can be a great–and free– way of reaching many people. Also use your current clients to network (they could “bring a friend” to help your marketing). Perhaps you could offer a free class or two to spark interest in your program.
Hope some of these suggestions help.
With this type of thing, referral is always the best method for marketing.
The best way to do this is:
1) Start small by leveraging your current network like people you already train
2) Do everything you can to make sure you your clients have a GREAT experience
3) Give them a means and motivation to refer
A means to refer is obviously word of mouth which you don’t have to provide, but try creating a facebook page or a short website with your training services info and share this link with your clients. An email to a client asking for a referral with a link to your site can go a long way.
Then, you can provide additional motivation – for example, for every new paying member a current user brings they get 2 free training sessions.
Hope this helps and best luck!