Hi @Sarah141 the best prebooking messages for me includes these information:
1) The purpose of your travel - As a host I don't want people coming to party hard and get drunk in my place. I like people who are traveling with family for sightseeing and food.
2) You have read the listing description - Every time a guest books I don't know if they thoroughly read the listing description which irks me because if they missed something out, they'd ask for a refund or create problems later with additional requests. Worse they write a review about something bad which was already addressed in the listing.
3) You are clean and responsible - Hosts don't assume this, and if you have no reviews it's good to make this claim because it shows you are aware that it's very important
4) Let them know your interaction style - you like to chat and hope the host will bring you around, or you're looking for privacy. This sets expectations from the onset of how the host should treat you during your stay.
5) Let them know how many adults/kids are coming - just so I know you're being honest with the guest count here.
6) Sound friendly. Say Hi how are you or something. Compliment the place if you like it. Not something like "eat food, sight see". We're humans too, not just a house.
Hope this helps!