This is to be an indoor range, right?
Location, location, location. That said, if you cross the threshold of bad customer service, you'll never see me again.
Of course, the strippers hang out at the tourist range...
In addition to location, having something to offer like American Shooters doing their monthly evening matches for IDPA and USPSA. Even if you didn't offer a sanctioned sport, it brings people in. Heck, American Shooters should lose their sanctioning anyway. I quit shooting their matches because of the cheating and safety violations from their staff.
Offer a good deal on a membership. Someone using your range doesn't cost you much, relatively, so a membership is a win-win. They will tell their friends what range they are a member of. They will buy ammo from you. Some of them will leave their brass. They will always check your shop first for guns and supplies and transfers. So make the membership affordable. My $350 for an American Shooters membership was too much, even if I hadn't gotten ticked off at some issues and stopped going after only a few trips.
Oh yeah, and have a go-to instructor available...
Plan for growth. Once you commit to building the range, spend a little more and make sure you have enough lanes available, and make them wide. I would spend extra not to be cramped, even if the place wasn't always full.