All of these are great answers. Below are a few more resources you might want to check out prior to launching:
The 2014 SEO Checklist by ClickMinded: I can't endorse 100% of everything on there (we all have our own opinions, tools and methods) but it is a fairly comprehensive checklist.
The 2013 SEO Ranking Factors Study by Moz: This is from last year, but still relevant and mostly accurate.
The Periodic Table of SEO Success Factors by SEL: I find this visual format very confusing and convoluted, but others find it very logical and easy to interpret. I think it depends on the person. I'm more data-oriented rather than visually oriented. Either way it's a good resource.
The biggest mistakes I see on eCommerce sites are as follows:
- Non-Unique Product Copy (e.g. Content taken from manufacturer or distributor descriptions, or product feeds)
- Internal Duplicate Product Copy (e.g. product variants with their own canonical URLs using the same copy, non-canonical URLs created by query strings, from products in multiple categories, etc...)
- Thin or Useless Product Copy
- Indexable URLs for Filtered/Faceted/Layered navigation
- Indexable URLs for internal search results
- Indexable shopping cart URLs
Good luck!