Think of all the things we make fun of...and dublicate them.
The best gym I was ever a member of was a mainstream place, but in a small community:
Main floor mostly machines, such as Hammer Strength. On one wall all the dumbbells were lined up, multiple sets of light DB's on one side and on the heavy side cages were segregated. People want to see guys lift heavy but they don't want to be around them.
Bench presses were on the other side of the floor (with the machines), everybody uses these as well.
Up stairs all cardio and a circuit training section. Middle open to see the weight area below.
Interesting point- The owner used to buy a new machine (or two) every few months and either ship a machine or two to his other gym or sell it to another gym. People were always lining up to use the "new machine", no matter what it was.
Oh yeah, don't forget atmosphere, make it bright, pop music (not too loud), TVs in the corners (sports are good), tanning beds and a great bar/apparel shop.
As for cleanliness, have an employee constantly going around cleaning equipment, women make up about 60%-70% of the clientele of most fitness centres and they notice people cleaning, especially if the person is obviously working hard and keeping the place clean...they will also notice if the person is only socializing and leaving equipment filthy.