One of my stores, www.Gothicplus.com is in the top 8 results on google for 10 keywords- for 5 of them, I'm #1

I only use Opencart's 1.5.2 built in seo tools, no seo addons.
So how did I do it?
I took some time to develop a list of keywords I wanted to rank for (using google's keyword tool to see what was being searched for in my niche) and use them throughout the store - in product names, descriptions, meta data, category names, tags, etc. Most products have descriptions I wrote and probably 70% of the products on this store I also list on 1-3 other stores - the others are unique to it. I've been working on backlinks from dofollow and nofollow sources like forums, blog comments, etc, for about a month now. I have product feeds with google and thefind. I did htaccess 301 redirects for my most popular products and those that were posted on pinterest, etc. I have facebook page, G+ page and twitter accounts for it. I submitted my site maps via google and bing webmaster tools (using UKSB's feed extension). Not sure what helped the most, but I would highly recommend doing all of the above.
I've never done PPC or any other paid marketing or linking schemes and I try to find blogs and forums to comment in that fit my stores niche. I do not have a blog or youtube channel for this store, though do post products to pinterest and bookmarking/product discussion sites. I haven't created any static pages for the store either - it uses all opencart dynamic pages. Haven't done any article submissions for it either.
The opencart version of this store only went live in April (original store was up since 2004), so getting #1 rankings in only 4 months I'd say is pretty good
