I'll second scheduling at hours outside the 9-5 range that most people already occupy with their own job. The one public darkroom I could use here opens until 10PM on Thursdays. If it also opened on weekends that would be even better.
A small detail that made all the difference whether I use a public darkroom or not was ease of registration. No kidding: at Université de Montréal, there is a super narrow window of time at which you can register, like Fridays AM between 10 and 11:30. Utterly stupid. If I can't register by phone, pay by credit card or at least at the time I use it, and move my ass only for the purpose of using the darkroom, then I am not going. Sometimes people just fuss around payment for some reason (buy your credits first but you can't do that while the darkroom itself is open because the employee is not available, blah blah). Getting into your darkroom should be as easy as getting tap water.
Other ideas: solid and well-maintained equipment; some variety in the enlargers choice (condenser/diffusion/dichro heads/cold light), at least one 4x5 enlarger, depending on your clientele; that could also involve a sheet film development solution (trays/tank/other); a light-tight space to load film on reels; large trays; good print tongs (!); contact printing frames; an east setup for drying FB prints overnight and not getting them stolen or lost; 5000K lights viewing area; light table; drymount press setup; lockers; revolving door between darkroom and viewing area; some space to tone prints; the ability to use a different developer from the main one (i.e. space for another tray); everything at 20C (aircon in summer!); a choice of standard film developers (e.g. XTOL, HC-110, Rodinal, PMK, Acufine, Perceptol); the possibility to buy either paper/film/chems through you if you can have them discounted at edu price; lots of spare equipment (reels, tongs, trays, tanks, etc); a few reference books (Anchell & Troop, Roger Hicks, Les McLeans, Ansel Adams, Phil Davis, Barry Thornton, Hedgecoe, etc); a computer to post on APUG while rinsing the prints and a small cabinet to keep the Cabernet.