First thing you need to do to develop any business (or online business in this case) is deciding your business model, and target market. I'm no expert in this field, but personally I would recommend to choose fields that suits your personal interest. Lucky for me, my education background is in Information Technology, which also happens to be my personal interest.
My first step in this case is having my own IT Consulting company; hopefully it could work and grow. Basically it's just a holding company for my product, School Information Portal. I choose application service provider as my business model, and the target market is schools, specifically international schools.
My product, Smart, is basically information system in form of a web portal that allows students, teachers, parents, and head masters to share information, such as scores, announcements, materials, etc, and collaborate in forum discussion. I choose application service provider model, because I think it's better to have long-term relationship with my client, and have a recurring income. I choose it over traditional software sales, which will only generate single-large income, compared to smaller-recurring income from ASP model. As the trade-off of the business model, I offer more services to my client. I handle all the hosting, maintenance, and software development for them.