Your website might have loads of content, but unless it’s been written with SE’s in mind it’s likely that it’s not being ranked well. Search engines live content that has been search engine optimized, or SEO‘d. However, the search engines will only give you good rankings if the content has been written in a way that both people and search engines will be able to read it. This realization, along with the changes to your current and future content, forms the building block of a primary SEO strategy:

Content is, was, and always will be, king. Good content will bring back visitors, draw in search bots, and help with your rankings. I cannot preach this fact enough.

Without getting into tremendous depth about the ways that Google (and other top-tier search engines) will index your page I can provide a few important points:

1. Use title tags - It has been shown that Google and Yahoo give text placed in title tags (H1, H2, H3, etc.) more relevance than just text alone. Use a style sheet to have the title tags reflect your desired look and use them when appropriate, incorporating your targeted keywords whenever possible.
2. Bold, italicize, and get attention - There is good reason to believe that text that is bolded or italicized are given a better ranking than simple text alone. This is likely because Google sees those as more relevant as they are emphasized on your website.Bold/italicize when appropriate.
3. Maintain a keyword density of no more than 6% - Having every second word read as your keyword is annoying to both visitors and search engines. Visitors are far less likely to actually read the text, and search engines will see it as keyword stuffing and penalize your rankings. Obviously, you want to avoid both of those.
4. Avoid images when possible - Though necessary to maintain a graphical interface and a pleasing design, avoid placing important text or titles in images. Search engines are unable to read the text within the image, and hence are unable to rank your website appropriately based on that text, even if it is a keyword.Modifying your style sheet so that the text appears as you intend it to will give your SE rankings a boost and will take less time to load up on a visitors computer (believe it or not, but the majority of internet users are still on dial-up).
5. Everything in moderation - Over-optimizing your website will lead to long-term search engine ranking loss.  Remember that the search engines are all about the user experience, and if they feel that you are not offering an acceptable user experience they will penalize your website.

With that in mind, optimize enough on-site, and then focus on off-site optimization, such as link building.  One you’ve got traffic coming to the website the task falls on your content to keep them there and interested.  Mastering that, of course, is the whole point to the game now isn’t it?