Most people I've worked with to create their own ethical will have included a section about their beliefs. If you'd like some inspiration for writing and giving voice to your beliefs, take a listen to (or read) some of the essays from the "This I Believe" program on NPR:
This I Believe
After you've written your beliefs for your ethical will, you may want to contribute some of what you've written to the radio program. They've made it easy (once you get through their "submission agreement"). I haven't contributed myself yet, but have added it to my "to do" list for some day in the future.
Let me know when to listen to your "This I Believe" segment on our local NPR station.