Be careful. Most SEO advice stems off of old advice that was just plain wrong when it was written. It seems that much of the SEO world cannot grasp that SEO has become much closer to what it should have been all along. As well, this is a follow the leader industry even as the lemming leap off the cliff.
I will give you a quick SEO rundown.
For each page, quickly jot down the most important 2-3 keywords for that page. Create a second list for each page that are the second most important keywords. Limit this to another 2-3 or so. It is okay if you want to write down 7 or 8 or more. Do this for reference. Since your site is coming from a database, then much of your keywords will be somewhat automatic, that is, product name, manufacturer, etc. It is okay to actually skip writing these keywords down if it makes sense. You just want to create a plan of sorts. Some people like using a spreadsheet and saving it for future reference.
Create pages for humans and not machines. Make sure it is natural and helps the user more, if possible, than anyone on the net.
title tag is the most important thing to pay attention to short of links which we will get to.
Title tags should contain your 2-3 most important keywords. Again, this can be automatic depending on the software you use. Make the
title tag conversational and compelling. The
title tag should be roughly 50 characters, but the limit is actually 512 pixels in Google. Bing is more forgiving. You may need to limit your
title tag to less than 50 characters if there are enough wide characters (W, M, Q) to expand past the 512 pixels. You have to remember that the
title tag, if done correctly, will the be the search engine result page (SERP) link. So make it appealing and motivate your user to click the link.
description meta-tag is the second most important thing to pay attention to. Again, this must be conversational and compelling. The
description meta-tag, if done right, will be the SERP snippet. It should have your 2-3 most important keywords plus a few from the second list. Your goal is to have a 2 line SERP snippet. It is okay if it is one line, but it will not likely perform as well. It is also okay to go to three lines, but do not push it. Your
description meta-tag should support both the
title tag and
h1 tag from a keyword perspective.
Your one and only
h1 tag is the third most important thing to pay attention to. Again, conversational and compelling. But in this case, you can also think headline if it applies. Again, use your 2-3 most important keywords and one or at most three from your second list if you think it works. Your
h1 tag should closely match but not be identical to the
title tag. The
h1 tag should support the title tag from a keyword perspective.
Any other header tags (
h4, ...) should support the
title tag, but also set themselves apart somewhat. Think of these as portions of a larger topic- How To Bake Bread would have Ingredients for Baking Bread, Mixing the Bread Ingredients, Kneading Your Bread Dough, etc. You will be keeping one eye on the 2-3 keywords and using keywords from your other list more. This is your opportunity to wedge in those keywords from your second list if it is natural to do.
Keyword density was never really a myth, but somewhat a myth. The recommended percentages were ridiculous. If you followed the density advice given, your content would be unreadable. Today, keyword density can still be seen to work on some sites (I answered a question or left a comment recently regarding eBay pages that performed well mostly due to 2 word keyword density), however, it is a Google no no and these sites are being targeted very aggressively with Panda 4.0 and 4.1 and likely soon with 4.2.
So don't do it!
Internal links. Each internal link must use the most important keywords for the target page. Since you have a store front, this might be automatic. However, if you use links within content, make sure that they vary somewhat and are conversational and fit within the content. I have several sets of links to pages; navigational, page title links (reads like an article title), and content links that can be used within content.
Inbound back links. You will not have control over most of the inbound links of course. But for the ones you do have control over, you do want to vary them as much as possible and make them conversational if possible. You do want to use the 2-3 most important keywords most of the time, but a large portion should also avoid this. For example, TMS Laptop Model 1234 v.s. Here is a great laptop for students. Your second list of keywords come into play here. Where possible, if you can get a conversational link within content that will be great but unlikely. So do the best you can. Just make sure that the linking page and target page are complimentary in topic. The link must make sense.
And never, never, never, seek a site-wide link and especially a link in the footer of a site. Make sure the links you create are natural and made for humans and not machines.