1.  Good marketing - People need to know you're there.
2.  Community involvement - People need to know you care.
3.  Good food - Not just a frozen burger to tide people over.  
4.  Good drink - at reasonable prices.
5.  Good people (working) - Can't just be a lump handing out balls and taking cash.  Needs to be part of the good marketing.  Friendly, helpful, etc.
6.  Good people (playing) - Having the wrong demographic will scare away the others. 
7.  Great equipment - no brainer.
8.  Good leagues - as many as can be supported well from both player and LO support.
9.  Good supported tourneys - Whether weekly or monthly, needs to be marketed/handicapped to keep lesser players coming.  Too many times tourney's die because of the same winners over and over.
10.  Kid leagues - Get involved with local kid programs and start a kids league.  Ran well, this will add $ to your coffers and grow the sport!  Parents come with to watch their kids compete, have lunch, etc.  Then the parents realize it's not just a hangout for the bad kids.
I'd be interested in feedback on my Top10 from players and former room owners as I may be getting ready to open a room.
What was their best investment?  What would they do differently?  What caused the closure (besides not enough money)?  Was it bad location, no food, no drink, bad people?