Community gardens need a strong supervisory team. I would suggest getting two others who are interested, drawing up guidelines about communal use of water/tools/mulch or compost, and laying out the plots before letting anyone sign up to use them (cuts down on complaints about size, sun exposure, etc.).
Then, have a contract that each gardener signs, agreeing to be neat, not plant tall crops like corn that will shade the next plot's tomatoes, clean and put away communal tools, and participate in a spring and a fall clean-up day.
Before the gardening season starts, have a meeting where everyone meets the other gardeners, the rules and expectations are explained, and any questions are answered. I also strongly suggest that you have a minimum fee--even if it is $10--because people value what they pay for more than what is free.
Then, when the season is over, have a pot-luck communal dinner and congratulate everyone on a great gardening season!