What is the fastest way to obtain clients when you train at an apartment gym, client homes, outdoors, etc.?

I just started out in January 2017 and am having trouble getting clients. My focus is mainly on athletic training. I personal train part-time in the evenings in the weekends as I am a full-time CPA. I’ve been using Thumbtack and have obtained one client off it. Any other advice/ideas to get more clients?