I no longer make eBay my main focus for sales, it's mostly a branch of marketing now.
1) Don't focus too much on the actual setup and storefront. Just use something like Magento, Prestashop, or hell, wordpress and the ecommerce theme. It doesn't really matter on a starter level. People will go back and forth all day about which is better, but chances are they have never set anything up themselves.
2) Mock up a cool theme that is VERY simple. Simple is good. Complicated is not. You can even use MSpaint, pay someone $20 to make something that looks a little better, and then hand over some detailed plans on what you want to do to an actual designer who can develop a website from you. A simple site might only cost you $50, a little more detail I would plan on spending about $200.
3) Upload your inventory. Pretty simple. Unlike eBay, professional looking photos look good, convert well, and show relative size. Things like getting good photos taken of a small child holding a pillow you are selling is cheaper than you think and convert very well. You focus a lot on conversion rates and stuff once you have your own sites.
4) SEO, if you don't know how to do it... hire people. I hire westerners, I've been though probably 50 eastern SEO companies and don't really have any good stories to tell, I'm just not too impressed. I get an SEO team from the U.S. on a project, its usually done quicker and I get better results. Don't skip out on this. People think that they can skip out on marketing, but you can't. In the beginning your marketing budget is going to be pretty high. If I started a site and I brought in $10,000 my first quarter of profit, I would probably reinvest $4,000 of that on further advertising until I get to a position where you are more sturdy about the traffic coming in. Once you are comfortable, don't decrease your budget, just do not increase it and see what you can do to get a bigger bang for your buck. You need traffic.
5) Give more. You have to. People have raised the bar to some crazy level where you cant just offer great customer service and a great product for a competitive price (You can't be Hank Hill). You have to give more. Upgraded shipping, free promotional items to bring customers back, snail mail coupon codes, etc. Look up Zappos videos. I even send out birthday cards and free small items (like a Luigi Key Chain or something). You are going to realize that a lot of competition is going to come and go in whatever niche you are in, you will also notice that a lot of your competition has little to no experience, knowledge, or back up capital. Use these "Lack ofs" to use your advantage by increasing your marketing on a ground level (forum marketing, youtube contests, etc)
6) Actually give a shit about feedback from your customers, and forget formalities. If a customer calls you up asking a question, don't go "Hello, thank you for calling _______, I will locate your package as soon as possible. Yes Ma'am, No Ma'am. Thank you." - People don't like formalities, people want their experience with companies to be personal and relaxed.
