I have never done one , but I would put something like.
How much you will charge.
How long the contract is for .
What notice you want if they want to cancel.
How often you will clean, I would list the dates then they know when you will be there next.
How payment is to be made, cash / cheque, on day ,or x days from invoice.
When your next price rise will be .
As I say I have never had to do one.