Matching Phrases to Pages
Now that you've got your keyword phrases take a good hard look at your existing pages and work out which ones are already using these phrases and which ones aren't. Try and match each phrase to a page and see how they stack up.
Are there lots of pages that all match the same phrase? If there are, how are these pages related to each other? Are they scattered throughout the site or do they form a reasonably cohesive unit. You'll need to decide whether they can be made to help each other and whether they can be arranged and linked to concentrate the relevance for their phrase onto one key page which will become the main target.
On the other hand are there phrases with no matching pages? If that's the case then you will have to write new content - either adding to pages which are broadly relevant or writing completely new pages. If you don't do this then you will never rank for those phrases. At this stage it's also worth asking yourself why you have no pages corresponding to those phrases - are they really that related to your business? If they are how come they weren't already mentioned? It could tell you a lot about the way you've been handling the development of the site and how the decisions about it are made.
Navigation Matters Too
You should now look at your navigation system and see if the links used in it reflect the search terms you've been working on. If not then the menus may need revised - potentially in terms of both text and structural heirarchy. If your keywords naturally fall into various categories then it will often make sense for the site and the navigation to be structured in the same way.