How to set up your own drama school
This entirely depends on the age bracket your classes are aimed towards. Probably the easiest target group would be 5-18 year olds, as such your drama school should be based around after-school age-defined classes, one to three hours a week. You could offer training, L.A.M.D.A graded exams, and perhaps put on 1 or 2 performances at a local theatre each year. Pupils (or their parents) would pay per term. This is probably the most easy approach to opening your own school, as you would attract more potential pupils; children have a lot more spare time to join clubs and drama schools!
You would need to locate a suitable venue, anywhere from local town halls to theatre's or studio space, decide specifically on what services you would like to offer, come up with a brand, hire staff, and promote your new school. Promoting the school can be done fairly easily if you're attracting pupils who are still in full-time education as you can send information and leaflets to all primary and secondary schools in your area, perhaps offering a free 2 week trial to all pupils who attend. Yourself and any staff you hire would need to be CRB checked, if you hold a PGCE it would be beneficial and make the legal process a lot easier. You would need to set up a business bank account, plan your curriculum, come up with a business model etc. If you were wanting to set up a drama school offering full time training, and BA qualifications or higher, the easiest route would be to offer the course through an existing local college or university. Getting the rights to award high level qualifications independently is a lengthy process, so it would be wise to work along-side current well-known establishments, and seek independence a few years down the line once you have solidified your own reputation.
It surely goes without saying but previous teaching experience is a must, if you have not already done so, I would recommend that you spend a few years teaching drama or acting before embarking on establishing your own school.