Make sure you have a lot of foot traffic, and a good local community of pinball fans (which will grow as they play more and more machines). Be ready to not make much money and work long hours, especially at first. Also be ready for endless maintenance issues on a daily basis, if you cannot fix just about everything or have someone who can (for free, or very cheap) forget about it because you will be awash in repair bills. Also make sure you have a large variety of games, and understand that the newer fancy pins will always earn more. Also be ready for overly anal pin collector types to come in and tell you how you have a bulb and how your game is not as perfect as the one in their basement like they are some kinda pinball super hero or something. Also get used to (some) kids that think they are playing a video game and hit the flippers endlessly from ball launch to ball drain as fast as they can, sure it may be funny at first but again this only adds up to more maintenance for you (see above). Make your place as comfortable as you can for people, so they stay longer (and spend more). So offering drinks and snacks is a good plan, and getting a beer license is a great way to make extra money (beer/wine only, I would avoid full liquor for many reasons).
League and tourneys are pretty much a must. It took me a while to get this off the ground as the local community of players started to grow so did the league. I would schedule these on your slow nights, so that way you have a nice quarter income on a night when you would not have otherwise. Also contact the guys at ifpa so you can get WPPR points to your people which will get more people interested. Also I would find a place with electricity included, it is kind of important.
hope this helps and good luck.
fmpinball.com
p.s. don't open in my town, or we will be forced to have a rumble. 
Stockton, CA
