First of all, I’d get this book, but I’m biased. http://amzn.to/2ddYRRC. I have a sample marketing plan worksheet in there already started with a bunch of low or no cost things you can do when starting out.
As far as building trust to get more leads and clients goes, you may not have many or any clients to start out with. In that case, have a few people you train for free or are bartering for something else. Preferably people who are trying to lose a significant amount of fat. Work for the best results you can in them and their friends will notice and ask and they can refer you. That’s a little longer term though.
Business wise, the most powerful thing I think you can do for trust is networking in person. Check your chamber of commerce, BNI, Meetup, etc. for local networking groups and attend them. I have a process in the book for how to go about it, but basically, it boils down to making friends in business, getting them in to try a free consult or to view a demo of what you do, and signing up those leads. They may be leads themselves, but really, the value is having a bunch of business associates out there in the community acting as your referral partner. These groups also allow a member to do an elevator speech introduction each meeting and 1 or 2 members to do a longer 10 min presentation or so. If you can get to do one of these as soon as possible, it will reduce the curve in obtaining their trust. Of course, be really trustworthy!
There are other ideas, but that is one of the more effective things you can do. Good luck!
Business Tools and Resources for Personal Trainers