Angie
Hey David Dutton here...
As someone who does keyword research for people as a service, I can share with you what I do personally and have my clients do.
Hopefully it will work for you.
I am a very visual person. I like seeing the BIG picture.
What I do is create a mindmap of my entire site using a software
called Mindjet. It isn't cheap but I am addicted to it.
If you google "free mindmapping software" I know there are some out there that will be just fine.
If you do not know what a mindmap is then here is an example.
http://www.mindmapexample.com/samples.php
You can do the same thing on a yellow pad but I like using my computer.
As far as keywords....
1) I take my main keyword and put it in the middle as my main topic.
2) Take 5 secondary keywords and draw five circles coming out from my main circle. Those are your teir two pages.
3) Take 5 more keywords and have them branch off from each one of your tier two pages.
Does that make sense?
Once you do this you will feel like a million bucks because your site sturcture or "bones" as I call it is done. Just add the content.
I do this with ALL of my content sites. I just did it with my greeting card site this week.
If you have any questions then please don't hesitate to ask them.
Dave