As was noted above, there are three types of searches. To optimize keywords correctly you have to do quite a bit of keyword organization before you begin optimizing. Make sure you group your keywords by category and then segment further, as needed, to ensure you have only tightly related keywords in a single keyword group.

By grouping into the categories, you can make sure that your content matches the searcher's intent. You only want informational keywords optimized on informational pages, and transactional keywords on pages where something can be purchased, etc.

Then by segmenting them further you're ensuring that your content can be very focused not just on the overall intent of the search but on the specifics of the search, as well. You want to be able to write content that engages the searcher, providing them with the information they need and not a whole lot more. Depending on the keywords and type of search that can mean a lot of content or very little. You have to figure out what content will best do the job of converting the visitor into a customer.