Right now I'm renting space from a judo/ju-jitsu dojo for one night a week, when they would normally be closed. If we get more people, we might be able to expand the classes to two nights per week. We started with two students in the area and now have an average class of five.
Perhaps this is too basic and you've already done this. Write up a business plan and a maketing plan. I've found the numbers for dojos are hard to find, but you can guestimate the figures. Looking at other MA schools in the area can give you an idea of the market situation.
I've just finished the business plan and have started working on the marketing plan. I wish I had thought of this when I started a year ago.
Good luck with your dojo!