Creating a structure that works for the search engine spiders as well as your visitors is the ultimate balancing act. But if you ever want to lean to one side or the other ALWAYS lean to the side of giving the visitors an excellent experience.
With that being said here are some structure principles to live by; Usability – Build your site for visitor usability and ease of use not just for spiders.
Page Penetration – Get as many pages ranking and being indexed on the search engines – the more that are on the engines the better = Page Penetration. Per the above structure principles lets dig a little deeper into each one;
The main thing to consider when developing pages is keeping your keywords in mind as you design and develop a web page and content; however, be sure to also keep in mind that a human user looking for a product or information will be reading and looking at your web page.
So always make sure you write for the human users before you write for the search engines. I would rather error on the side of making sure that the words and information on the page allow the user to have a great experience than have the search engines find it, index it and have a user leave the page quickly because it doesn’t make sense from a user standpoint.
Top Level – Your Index/Home Page This is the page most will see when they find your website therefore it needs to give them a “clean and clear” view of what your site is about and where they can go to get deeper information (secondhand third level).
So clean navigation and a clear overview is paramount to your success in keeping a new visitor on the site as well having them “click-though” to other pages and get deeper into the various levels on your site.