I've worked with some e-commerce sites before. I'll try and explain the way i handled it.
1. Know the opportunities and limitations of your CMS (Content Management System). I've worked with Magento and i did a lot of things by myself which were done automaticly by Magento. Such as creating XML sitemaps. Knowing what your CMS does for you helps you focus on the weak points of the CMS.
2. On page optimisation: An E-commerce site wants to get found on it's products in most cases. Are your product pages optimized? Make sure that all your product pages have a really good title and description. Not only for SEO purposed. Of course having your important keywords in there helps but make sure people would click on it too. Find someone from your target group and ask them about the quality of your titles / description. Would they click on it? If no, then why not. Use their feedback to improve them even more. Product descriptions should be really good too. This webshop http://www.vat19.com/ really knows how to create product pages which are aimed at their target group and contain a lot of content. The images and video's are rich media which are relevant for the target group and Google loves this.
3. Social: There are so many possibilities for E-commerce websites on the social platforms. Make sure you have a Facebook page, twitter account, Google+ account and Pinterest account. The buttons should be implemented on at least the product pages as well. Facebook and twitter allow you to reach your target group and get more exposure to other people. It is now even possible to include webshop functionality on Facebook pages. Google+ will soon get this too if i'm not mistaking. I mean they have Google shopping and they are making Google+ the center of all Google products with an added social layer. Pinterest allows you to pin all your products and recently they added the option of adding prices and stock to your pins.
4. Link building: As Takeshi said before this is an excellant list of link building techniques: http://pointblankseo.com/link-building-strategies. Make sure you have content that people want to link to. Some e-commerce solutions offer a blog next to the webshop and i know that there is a Magento plugin for making a connection to Wordpress. A blog is something to get a better connection to your customers and is great link bait by itself. If you do other things such as product review video's or so this is also an excellant place to gather feedback from customers.
I hope i helped you somehow and if you want more advice or if anything was unclear please let me know.
Good luck