Top 3

I was working on a whole list of things you should ask your MT, but it really comes down to a handful of things:
1. Are they certified?
2. Are they permitted?
3. Are they insured?
Certification happens from their school and comes after completing both hours in practical learning and academic learning.
Permitting happens at the city, state and national levels. California has just started permitting Massage Therapists and so far they do not require a written exam, but do require a background check and finger printing. The National has a written exam as well as finger printing and background check. City requirements change city-to-city. Clovis, where I work, requires a background check, finger printing and a written test.
Insurance seems obvious, but many practitioners don't carry it. Some think they are covered by the location they are working out of, some may be, but it is always a good thing to clarify before you get started with someone new.
Those are the key points to hit on before you start a working relationship with a MT, other questions you may want to ask:
What type of products do they use? This is important because not everything is hypo-allergenic or Paraben free. This is especially important if you have any allergies or are sensitive to smells.
What modalities do they practice? If you aren't familiar with the modality they practice, google it. You might be disappointed if you were hoping to really dig into some of those tight spots, and your massage therapist practices Raki, like wise, if you just want to relax and you end up with a deep tissue massage, you may be disappointed.
Just remember, it is your massage, keep communicating with your MT to get the massage you want.