OK so are you going to develop the site yourself? its gona be a hectic task and can't be taken care of alone unless you have friends or some professional helping out. you must decide on what you want to sell and to whom. its vital to be well aware of your target customers and then market your products to them only. saves on alot of time and effort so that you only approach the potential customers out there. Next you must consider on an ecommerce website that contains the shopping cart and obviously various paying option. its is advisable to keep a wide selection of payment options customers can choose from. they prefer it. you must assure in-detail information to available to your customers regarding the products you are selling, that could include upload images or specifications about them. also while designing your website, do consider making it user friendly, easy to navigate,less complicated and cluttered up. Another suggestion is to keep a live chat/messenger option on your website for customers to communicate with you in real time. Last step is of SEO. that whole separate process altogether to make your website show up on the search engine results up high.