In my opinion, there are many important factors to consider before starting an e-commerce business.
The first and foremost is to understand your product and analyze whether it is feasible enough to sell your product online and make some profits or not. There are many ways to do the same.
I have written in detail on the topic Things to Know Before Starting an e-Commerce Business and you can download a free preview for the same at http://www.atuljain7.com/things-to-know-before-starting-an-e-commerce-business/
Hope this helps