Apart from specific cases, don't forget to empty the grey water and cassette, fill up the clean water tank and refill the fuel tank.
Give the vehicle back as clean as it was on the first day: consider the owner and the next renters! The cleaning steps will also help you ensure that you didn't forget anything inside the vehicle (bedding, games and any other personal belongings). If the vehicle is in any way dirty (outside or inside), the owner can ask for compensation in order to clean the vehicle, and this will be noted on the rental agreement. The penalties highlighted in the clauses of the rental contract apply in the event of uncleanliness.