Websites should be focused around closely related products or services in order to optimize for search traffic. The website should be focused on a single subject for the best results, but that is not always practical.
When you have multiple offerings, you need to organize your website into a clear structure that the search engines will understand. You should group very closely related topics into themes. In a website you can have keyword phrases, topics and themes.
On any web page you will introduce your keywords in the first paragraph. When keywords are used in all the paragraphs on a page, you have a topic. A group of closely related topics form a theme. A website may have 1-3 themes that are closely related.
Link Structure: You will want to link the most closely related topic pages together to form themes. To improve rankings for each topic page you can write articles and place them on your website. You can emphasize the individual topics by linking articles written around specific keyword phrase.
Example
Let’s say you have a residential landscaping business. You offer landscape design services and landscape maintenance services. These two groups of services are closely related, but should each be in its own theme.
Theme 1: The landscape design services theme could include topics for landscape design, front yard landscaping, back yard landscaping, installation of sprinkler systems, new sod installation, etc.
Theme 2: Maintenance services could also include topics for lawn mowing service, lawn aeration services, yard maintenance, tree trimming, etc.
When you have multiple themes, you would want to globally link the home page to the main landing page for the theme. Each topic would be interlinked within a theme specific.
Use your website architecture to connect very closely related content. This association helps the search engines determine relevance and you will be rewarded with higher rankings.