These aren't all from my current school, but some techniques I've seen in the past...
If something breaks, replace it with a new part. Although a new part is somewhat more expensive than taking time overhauling or repairing an old part, the savings come from less down time on the fleet. Faster repairs and better reliability in the long run. Cancel fewer flights, bring in more revenue, ultimately results in a profit. This technique works best for busy fleets. The busier the aircraft, the greater the loss from down time, obviously. I'm not sure it would be worth it for aircraft that only fly an hour or two per day.
Also, make it SOP to lean mixtures on the ground, lean in the air rather than running full rich in the practice area, and cruise at 2100 or 2200 rpm in the practice area, rather than 2400-2600 rpm. These techniques can save a gallon or two per hour which equals a substantial savings when multiplied across 4,000 hours/year on a fleet. That could easily equal $16,000/year!
Write in to the rental agreement that fuel purchased away from the home base will only be reimbursed up to a certain limit on a price per gallon basis. There's no reason to reimburse $6.00/gallon when you can refuel at the home base for $4.00/gallon.
Encourage a culture of safety, but also a culture where instructors don't cancel flights unless there is a good reason. I've seen instructors unwilling to teach in IMC, in VFR with rain, in winds greater than 25 knots, with ceilings less than 2000 feet, etc. All of these cancellations add up. Even when the weather is less than perfect, students can oftentimes benefit from coming in and doing pattern work, crosswind landings, ground reference maneuvers, chipping away at their instrument time, etc. Make sure your instructors believe in this.
Be willing to invest in instructor currency. The price of paying for an instructor's IPC is worth it, compared to having them cancel ten flights because the field is IFR and they aren't instrument current.
Make sure the instructors are billing for the time they're teaching (don't under-charge customers) and make sure the instructors haven't set up "under the table" deals with customers, such as meeting at a coffee shop for ground lessons and the customer paying the instructor directly without billing through the school.