Also, try to fly to as few destinations as possible. This will reduce your marketing and staff costs.
So rather choose a destination with demand to support 2-3+ flights per day than destinations that only support 1 flight. If there is another airline flying for example with 1 aircraft filling 60-70% demand, you can get most of it by flying 2 times / day, for example 70% for your 2 aircraft and 30% for the competitor with 1 aircraft.
However, you should also keep your routes short. For example, have 1 flight over night (arrival at the destination before 23:00 and departure before 0:00, so that the aircraft is back at your base around (after) 5:00) and all the rest so that you can fly 2-3 times, which totals to your aircraft flying 24h/day (including turn-arounds with <10% delay).
This kind of schedule is not always possible to do, but whenever possible, it's the best way to do it with short/medium haul aircraft.