SEO Internal Linking Structure

The honest fact is, if company owners knew how important that the internal linking structure of a site was to a site's performance on the search engines, they'd have multiple dedicated staff working just to make sure they had it optimized 100%. This topic is a little advanced, but it's helpful to break the inner linking structure down into three parts:

1. Page depth
2. Quantity of Internal Links
3. Quality of Internal Links

Page Depth

Page depth refers to the number of required clicks to get to a page from the homepage. Pages that are available in one click are deemed more important than those that are nearly hidden and require more than 3 clicks to reach. It might seem a little strange, but if you can visualize your website in a tree graph, you will easily notice why certain pages are performing poorly in the search engines.
By organizing your site in this format, you can see which pages are getting a lot of page depth love and which are hurting. If you have a lot of worthless pages and few important product pages, you might take this opportunity to restructure your site.

Quantity of Internal Links

This point is simple; the more internal links you have that point to a certain page, the more important search engines believe that page to be. A common page that ranks well on almost every site is the homepage. This point will continue to be true for many years because nearly every webmaster programs their site so that every page has a link back to the homepage.
So how do make your other pages benefit from this? Does that mean you should have every page on your site include a link to EVERY SINGLE PAGE in your site? No. That's an obvious red flag to search engines, and you'll be seen as a spammer if your site has a couple of paragraphs and then 500 links to every other page on your site.
A better strategy would to have a "Top Products" section that includes a link to pages you want to receive the most link love. Another strategy is to have a link for each of the major areas of your site. This will help give those areas a lot of link love, and in turn, they'll be able to get more link love to the pages contained within them.

Quality of Internal Links

Just including a bunch of internal links to an important page is not enough; they also need to be high quality links. For your most important pages, make sure the links they receive have as many of the following criterion as possible:

1. Anchor Text - If you're targeting a certain keyword(or keywords) make sure the internal links have the keyword in the anchor text. Also, bonus points for using slightly altered anchor text throughout your site.
2. Link Position - The higher a link occurs in the HTML, the better. If you link to "cowboy hats" at the top of the page, but "sombreros" towards the bottom of the page, search engines are going to view the link to "cowboy hats" as more valuable than the link to "sombreros."
3. Link Zone - The best scenario for link love is to link from one page to a highly-related page. The closer the subjects of each are in topic, the higher the amount of link love that will be transferred. For example, it is better to link form a page about "cowboy boots" to a page about "cowboy hats" than it is to link from a page about "tacos" to a page about "cowboy hats." This doesn't mean you shouldn't include links on pages that are different, but just keep in mind that the link love will not be as strong as it could be.