What essential clauses must be included in every freelance contract to protect against scope creep and non-payment?

[Btaliat]

Freelancers must make sure they block any loopholes that may happen while resulting with their clients. For instance, they need to take serious the contract they want to enter with their clients. For instance, they should make sure there is detailed scope of works to prevent any scope creep. There should be deadline and terms of payment. Infact there should be a way of handling intellectual property of the tasks. What else do you think?