First off you need a plan. Secondly, a plan. And third...you guessed it: A PLAN!
A plan doesn't have to be a long, leather bound manifesto, you can start at the beginning or the middle or the end but you need to have it down in some form to make a start (and to get a business loan) and you will need to be prepared to revise it as you go along.
Some basic elements:
1. A Mission: You will want to have a clear sense of what you will be providing to a potential customer (no, not the shopping ...other people already do that). What do YOU bring to the table as a vendor that will distinguish you from the competition.
2. Sales forecast: This is the backbone of your business plan: How much do you think you can sell? You'll want to research the market to get an idea for what the market value of your service is, how much time you will have for providing service, and what you think the demand for your service (in either a geographic area or area of Ecommerce) is.
3. Expense Budget: What will you need to spend money on to get started and keep going? *Hint: You're also going to want to compare this to your sales forecast...
You will need your ideas, research, feedback, and the right tools to organize everything into a cohesive plan. Consider springing for the new business writing software: http://www.liveplan.com/. It's clean, easy, and will help you get to where you need to be to get started.