Let's say that I host a website selling IP cameras, no need to worry about the quality, the after-sale services, how should I get started? facebook？twitter？pinterest？ dealsite？
You're basically asking "how to i get an eCommerce site off the ground" right? If that's the case, make sure your site is finished and working 100% before beginning any marketing. Once it's ready for prime time then basically do all of the things you mentioned in your post. The more free marketing you can do the better.
My eCommerce site is working for years by now, I really need some breakthrough. Is there any priority? how about affiliate program？