Open on a Sunday. If you can’t stretch to this, have a van full of pads, tubes, tyres, bolts etc and hang around the local trails, you’ll make a killing.
Maybe do a collect and return service for people like me who are too lazy to clean or maintain their bike. I would gladly pay for my bike to be picked up on a Monday and returned to me fully serviced and washed on a Friday, ready for use.
Make sure you have at least one blackberry or smartphone so you can answer emails and phone calls immediately. There’s no excuse not to be able to do this in the 21st century.
Offer everyone who comes through the door a cup of tea. If nothing else it takes 10 minutes to drink, and that’s 10 minutes of looking at shiny bike bling, they might even buy something.