It was just said. "Friends and relatives will be your worst customers"
All the info above is pretty good.
I do an Excell spread sheet outlining exactly what I will do and what will not be done. You can't get everything but as you go communication is the answer. The more detail the better. Most customers really like this. when we are done we can check off the items and agree the project is done as decribed.
I keep additional pages for labor and parts purchases as well as payments and other notes.