Summarize this article:

You want one that is affiliated with a national boxing organization and that also has a reputation for training fighters. If you are serious about this, do not go to a health club that happens to have boxing classes. You need a gym that's dedicated to boxing (and potentially other martial arts). Odds are if you do a bit of asking around, you'll find the place that has the reputation as the best of the best in your area. There will likely be no doubt about it which club you'd like to join. He will explain their hours of operation, fees and methods of training. You can also find out his experience as a boxing coach and whether he was a fighter himself at one point. Meet the staff and get a feel for the place. If it fills you with a sense of excitement and anticipation, it's probably right for you.  Do ask questions. Find out what they would recommend for you and what kind of training you should start. What's their schedule like? Who would you work with? How can you meet everyone? Make sure you know what you're getting into before you sign up. You want a club that has a wide range of clients at different levels. As you begin to develop your skills, you will want to start sparring with other people. A club with fighters at all different levels mean that there will always be someone for you to work with and that you can go grow with the club.  Think of it like walking into a restaurant: if there's no one there, you wouldn't eat there. And if there's only people in blue hats and you're not wearing a blue hat, you might not eat there. If there's only people who seem to be miserable, you probably wouldn't eat there. So take a look – do the clients seem A) fit and competent and B) happy with their training? If you can, find someone who doesn't work there about the establishment. Sometimes you need an unbiased party to get an honest opinion. Before you start working with a coach, it's probably a good idea to know at least the 101 of boxing and some of the terminology. You don't have to be good at it, you should just know a little of what your club peers are talking about. Here's a few starters:    Jab. This is the busiest punch in boxing. It's a simple punch thrown to your opponent's chin with your leading hand (the hand of the forward foot).  Cross. This punch is thrown with your dominant hand. It is a power punch. It involves a slight rotation of your torso, simulating a horizontal moment across your plane.  Uppercut. This punch ends up in your opponent's chin or solar plexus. It's thrown at close range and can be quite the cincher.  Hook. This is a short sideways punch delivered with your elbow out and to the side so your arm forms a hook.  Southpaw. This is a left-handed fighter (either naturally or converted). To a "normal" fighter, they do everything in reverse. Because of their stance differences, they practically fight on top of each other.  Outside and inside fighters. An outside fighter likes to keep his distance, stepping in for the jab. An inside fighter stays close, preferring moves like the uppercut.

Summary:
Choose a boxing club to join. Talk to a trainer. Check their membership. Familiarize yourself with the basics.