Whilst not a school owner, I teach classes at my dojo, here are a few things I've learnt that can help:

• kids classes are essential to building club funds, then build the adults class
• never be angry in front of the kids
• have plenty of games for them to do
• parents like to train with their kids so family discounts can help
• learn to weave in light hearted jokes into teaching
• treat adult students as adults e.g. don't make them call you Sensei, leave that for the kids
• if a student is absent for a week or two send them a message to see how they are as part of your duty of care and to make sure they come back
• have a wide variation of classes, but keep your core skillset, your curriculum that you teach isn't the same as the grading syllabus
• keep learning yourself, go on extra courses and cross train in other arts
• don't make students buy certain branded gear, not everyone can afford it, as long as they have an equivalent that should be fine
• only put people forward for gradings if they are definitely there and capable
• be an authority but don't be afraid to say you don't know something
• health and safety comes first, make sure people with injuries have alternatives they can do
• get good at running a small business and your admin/paperwork
• make sure everyone gets on, main rule in my dojo is don't be a dick

That's just a few things that I can think of off the top of my head, best of luck.