Sitemap - IntelliMap by AveA

Putting a quick sitemap together helps tremendously as it gives you a high level view of what you're working with. It also helps you (and the client, stakeholder, etc.) picture how each screen will connect.

I tend to create these before any wireframes or UI design.

This was done in omnigraffle.

UPDATE:
Please disregard the duplicate "Add POI" screen that connects to "Customer List" in this photo. That was taken in an earlier iteration and has since been corrected :P