1. Have very high expectations that they will be your coach, not necessarily your friend (though many of my clients have become my friends, my first responsibility is to be their coach and focus on their business growth).
2. Ask around to the people you know who have a coach, Google "business coach in (your city), or RSVP to the many coaches who have posted answers here (myself included: I offer a free strategy session to see if we're a fit, email brad@bradwarren.com)
3. Ask what their business background is, and are they a "pure" coach (who only asks you questions and never gives advice) or are they a hybrid coach (like me. I make a distinction between coaching, consulting, and training, and I do all three depending on what you the client needs).
4. Depending on whether it's by phone or in person, the frequency, their level of expertise, etc., the fees can vary from $400 to $2000 or more per month.
Hope that helps. Again, email brad@bradwarren.com for a no-obligation session with me over the phone.