You might check out the Adventures in FileMaking series. Adventures 1 and 2. They are free to download.
Adventures in FileMaking #1 - Conditional Value Lists (includes details on how to set up a basic field based value list)
Adventures in FileMaking #2 - Enhanced Value Selection (what to do when a simple value list won't cut it.)
The auto-completing search portals Demi's in #2 are a method I use in FMP GO.