What essential contract clauses protect freelance designers from scope creep and lat

[MichaelKM]

I've been freelancing as a graphic designer for about a year, and I've been burned twice now by clients who drastically expanded the project scope without additional pay or were very late on payments. I know I need a solid contract, but the templates I find online seem either too generic or overly complex for my typical projects. For other established freelancers, what are the most critical clauses you include in your contracts to protect against scope creep and ensure timely payment, and do you have a trusted source for adaptable templates?