I'm new to being a Massage Therapist. I have another job, which I do consider my regular job. As a self contractor, I was wondering what I can claim. When it comes to massage, I practice in one location (on average) but drive there from my other job. Am I able to claim that mileage? Gas expenses? Food costs while at my massage job?
What all constitutes? What should I be focusing on when keeping track for deduction reasons?

Costs that are directly related to the business. You will need to start keeping and tracking each time you use your car for tracking mileage, business use is deductable, personal use is not.
Your meals are not, but a business meal with a client or to discuss work can be.