Here's the 80/20 of getting the most out of a therapist, drawn from watching thousands of people get great results over the last 5 years:
* talk to several therapists on the phone for 5 or 10 minutes first. You're going to be hesitant and uncomfortable, it's their job to put you at ease, they're the professional. You'll learn a lot quickly about them, and about the mental health process. If you have an uncomfortable 5 minute chat, you're going to have an uncomfortable hour, so skip that therapist. Go with your intuition, either say "heck yes" or "no".
* make a plan, work the plan. Write out your goals. The way to do this is "present situation" -> "desired situation". Everyone forgets the "desired situation" because they've got so much negative mental energy tied up in "present situation". Anyway, take your goals to your therapist. Put a circle around the one you need to address first. Insist that it gets addressed, or 6 sessions will go by and you'll realise the only change is to your wallet
* ask for homework, do your homework. You're in therapy an hour a week and out of therapy 167 hours a week. Your therapist can't compete with that. What you do outside therapy matters greatly
* if after 3 sessions you haven't established a good working relationship with your therapist and seen a bit of forward motion on your goals, get a new therapist. It could improve but statistically it's unlikely. This is an evidence-based cut-off.
Mental health is health, stay healthy!