Well, KPJ, if you have any advice on that I'd like to hear it. Marketing is not one of my strengths.
What I do is SEO (Search Engine Optimisation). This can be divided into 2 categories - On page SEO and Off page SEO. Off page is backlinks, or inbound links (other sites linking to you). Backlinks are hugely important. In a competitive market, a website will not rank if it doesn't have a lot of decent back links, no matter what Google try and tell you. A link to your website is seen as a vote or recommendation i.e. you recommend site A to your customers / users by linking to them. The trick is to get your search terms in the anchor text, and some descriptive text surrounding it is good, too. The most important thing is the link, though. The best kind are the naturally acquired kind, which don't normally have search terms in the anchor text. Sites linking to you need to be relevant to your site, too. Or it's just a waste of time (if your getting them yourself).
As you can imagine, exrx has acquired a lot of good links over time. Exrx is one example of a site that can actually build links 'naturally' (the way google want you to), Wikipedia is another, T-nation another - Good useful content...
That's a basic overview of links, they can get quite complicated. Google are constantly catching on to new techniques and subsequently, they always move the goal posts...
On page SEO is where exrx thrives. The internal linking structure is brilliant. Plain text links (Search engines struggle to follow image links), loads of text, and good text at that. The places it could be tweaked is the tags.
Title tags tell Search engines what your page is actually about, this is one of the most important tags. So, as an example, you go to the store and look at the title tag, it reads "ExRx.net Store: Books, Videos and Software Solution" - There's no actual reference to 'exercise' their so it could be books about anything - as far as search engines are concerned. H1 tags are probably the next best thing, and the same applies with getting keywords in there. I notice from a quick look that the tags on this site seem to start with H2's.
Also, if you go to the anatomy page from the store and start at the title tag, 'anatomy' again is very generic. "Anatomy Books, Software, Anatomy Posters and Videos about Anatomy" would be more relevant - i'm rattling these off quickly, you basically want your keywords in as much as you can, but keeping it 'readable'. You'll notice some people just take the pi$$ i.e. Anatomy books, books anatomy, anatomy of books, books books anatomy... You don't get extra credit for that, just unnecessary.
The more you can link all the pages together, the better as well. Site maps are a usefull tool - a page with links to all pages on your site. It just makes it much easier for the Search engines spiders to crawl your site and store the information.
Unique content is great, too. People pay a lot of money for it. For example, in Travel, a lot of the resort / destination descriptions are the same. If you had your own unique descriptions, you would get rewarded accordingly. You actually get penalised slightly for duplicate content. Infact, it's so valuable that you literally sit and re type content and sell it by the page (I know companies that hire people specifically to do this, and could easily sell the pages). This is also why user generated content (wiki) is very useful. Loads of blogs, forums, news feeds etc are created solely for optimisation purposes.
You also have site structure... which is quite simple, the pages most easy accessible will get the most credit i.e. your home page (if you prioritise it, the search engines will, everyone prioritises their home page). So if the store is about 5 levels down the directory, it wouldn't do as good as it would if it were linked to from the home page i.e. exrx.net/store - I know it doesn't in exrx, just an example...
After that, you have conversion (converting visitors to buyers), which I can't comment too much on. I would need to see stats for the site and how users get to the site, where they land etc. it's all relative - what works for one industry won't necessarily work for others i.e some sites do well with 'cheap this, cheap that, discounts gallore' etc, but others do better with 'luxury this, luxury that' - depends on the product, price, margin and all that really determines the user / customer...
This could be somewhat 'all over the place' - now you know where my book long posts originated!