Need Help For Pricing

Hi my name is Rose my sister and i want to start a party decorating business our problem is we don`t know how to price something like this. Should we charge by the hour? or a specific amount say for 3 hour`s and how much. What about clean-up extra or include that in our price we would start with the basic just decorating an setting tables. If that worked we would get further into it with bigger decorations please help thankyou Rose