A. Find a few interested friends and get a venue (even a park) and start promoting the group until you are large enough to move into a better venue and become more organised. B. Find good venue and sign lease, pay several sets for mass advertising and promotional material to be printed and put out to you market base and hope you get enough students to cover costs in a reasonable amount of time (3-6 months)
advertisement is a must. fliers would really help too, make 'em fancy and inviting. you could also place your school online, i.e. yellow pages (basically, posting you dojo info online), a website too. will you be instructing in a rec center? thats also a decent place (pending on location) to teach, as many people go there. hope this helps.