As a cop friend once told me, "There are 100 ways to screw up a crime. A genius can think of 50. And buddy, you ain't no genius."
The same applies to business. Assuming you don't yet have a business plan, I definitely recommend that you start by going to the library and bringing home 3-5 books that deal with the subject. Read them all. Have your friend do the same. Sit down together and hammer one out. Take turns editing it. Keep working on it until it sings. Then start your business and keep writing new versions of it every year.