I would ask at an initial meeting how much experience they have in treating bipolar, what outcomes they've had, that sort of thing. The first visit should be more time to get to know each other anyway and those questions are completely appropriate.

I saw a therapist who was trying to learn as she went with me because she'd never treated someone with severe bipolar before. At the time I thought it was ok and then she moved away and I started with my current therapist who DID have experience with bipolar and it was like day and night. With him I work HARD at getting better; with her it was more supportive and we chatted more than anything. She was very nice and tried hard but she wasn't providing the treatment I needed. My current therapist can be someone to just talk to (like right now; I need to adjust to clozaril and the increased gabapentin before I am doing much work in there but he's making sure I'm safe and encouraging social activities when I wake up for more than 30 minutes at a time. So mostly we are just talking for a few weeks).

NAMI is a great place to find someone. The NAMI I went to had a list of good and bad providers and that might be helpful.