I also do mobile training and I must echo a lot of the things Susan said regarding scheduling of clients, travel delays and logging miles.
A few other things that I find are crucial:
A company policy covering everything you could possibly think of (attire, cancellation policy, late arrivals, etc). Because you’re working in someone’s home, a lot of more personal conversations and interactions can occur.
Decide where you’ll train. In their home, outside on a nice day or a local park. I like to change things up and will usually tell the client a day or two in advance where to meet me if its a change from our normal location.
A great lawyer! You’ll need an assumption of risk waiver and an in-home training liability waiver in case anything should break or injury occur in their home.
Review your home owners policy and your personal training insurance. There are some overlaps. See who covers your equipment if you take it to another location and something happens.
Document everything! Not just how the session went (reps & weight, etc), but where you trained, conversations, etc. You never know what might come back to haunt you.
Most of all. Be professional. I’ve had people meet me and say “what kind of workout could you give me out of my home?” Implying that it could not be anywhere near as hard as a “gym” workouit. I tell them to give me a chance. I just need 20minutes.
Oh, and keep your car clean! I can’t tell you how many times clients have followed me out to my car to ask me one last question or to grab a copy of an article or whatever. You want you car to convey that professional appearance as well.
Good luck to you!