In order to rank well in search results for a particular keyword phrase, your website must provide related information that is organized in clear language that search engines understand. When your textual information has been stripped away from its design and layout, does it measure up to be the most relevant aggregate information compared to that of other sites? If so, you have a high likelihood of achieving high rankings and attracting site visitors who are researching and shopping for products and services that you offer.
Using the analogy that most websites are like a jar of marbles, it is important that you create subject silos. A search engine can decipher meaning only when the subjects are clear and distinct. Take a look at the picture of the jar of marbles.
This jar contains black marbles, white marbles, and gray marbles all mixed together, with no apparent order or emphasis. It would be reasonable to assume that search engines would classify the subject only as marbles.
If you separated each group of marbles into its own jar (or website), they would be classified as a jar of black marbles, a jar of white marbles, and a jar of gray marbles.
However, if you wanted to combine all three marble colors into a single jar, you could create distinct silos within the site that would allow the subject themes to be black marbles, white marbles, gray marbles, and finally the generic term marbles. Most websites never clarify the main subjects they want their site to become relevant for. Instead, they try to be all things to all people.
Your goal, if you want your site to rank for more than a single generic term, is to selectively decide what your site is and is not about. Rankings are often damaged in three major ways:
By having too little content for a subject on your website
By including irrelevant content that dilutes and blurs your theme
By choosing keywords that are not well matched to your theme
Do you have your themes poorly defined, spread out in pieces over a number of different pages? Or are you mixing dissimilar items together on a page so that no central theme emerges (similar to the first jar of marbles)? Both of these cases may be preventing the search engines from seeing your web pages as relevant to your keywords.
If your website is not currently ranking well for a keyword phrase, consider both possible causes. You may have too little content for a theme, in which case you need to increase the number of pages that contain keyword-rich content on that subject. Conversely, if you have irrelevant or disorganized content, you might need to consolidate your subject themes by separating and concentrating them into silos.