Online business is a pretty vague term that is used to describe a number of different things these days.
The main things to identify in the beginning are what type of business you're attempting to create. Answer the following questions:
1. Is this an online extension to a previously established business?
2. What are you aiming to sell through the web site?
3. How will you get customers/visitors?
4. How do you anticipate making money?
If you can answer these questions further, we can definitely get into some more specific things to consider!