I've been meaning to write about this topic for a while, and it's taken me longer than expected to finish. A lot goes in to finding a personal trainer. There are a few super important factors that go in to choosing the right fit, so before you get one make sure you read through these.

1. Availability
You would think it's weird that I put this as #1. The most important thing when it comes to finding a trainer is finding someone who can train you at the times you're available (choose a realistic time where you aren't cutting it too close). You might fall in love with a trainer, but if your schedules don't match up it won't be a good fit,

2. Personality
This person isn't only your trainer/coach, this is someone who you are comfortable talking candidly about insecurities, goals, sometimes work stress or relationship issues. They may become your friend, so pick a trainer who seems "cool" and someone you truly vibe with off the bat.

3. Training style
Before finding a trainer, try to make a list of what you're looking for. Do they have a degree in exercise science? What about specific certifications (TRX, CrossFit, Olympic Lifting, HIIT). What's the trainers background (bodybuilder, college basketball player, or lost a lot of weight in their past). Do you have an old injury and need someone with a physical therapy background? Be ready to ask these questions.
You need to also chat with them about what type of coach they are. Are you someone who wants a drill Sargent, someone completely focused on form and movement, someone bubbly and fun, or someone who is more calm and understanding after you've had a long day. These are all things to think about.

4. Price
Trainers aren't cheap. 9 times out of 10 what you are paying the trainer is no where near what the gym pays them. That being said, make sure you budget for a trainer and if you want a specific number of sessions to let the trainer know/prep so they know how to program workouts accordingly. In SF Bay Area anywhere between $80-$120/hour is normal. 

5. Goals
After chatting with your trainer about your goals, make sure they understand them. A great trainer will know what you need to do to get there. A lot of time homework is given out. It's on the client to make sure they are doing what's asked of them to achieve this goal. For example, if you're a basketball player, but you never practice your shot on your own time then a lot of your time that would be used to progress you to new things will be wasted since your shot is so off.