If your child fails to clean their room, put a privilege on hold until a certain part of the room cleaning task is complete. For example, if you decide that today all the clothes need to be picked up, don't allow electronics until that's done. Or, don't let them go out with their friends.
I always would choose my battles, and their room being cleaned was a battle I wouldn't get into with them. With that being said, the rule was if anything started crawling down the stairs or into the living room, then I would go clean it without question. If I cleanned... everything on the floor goes in the trash or to the thrift store no matter the cost. My son challenged me on that one time. And, I did exactly what I said I would do. His room was always passable since then.
I used to tell my daughter that she couldn't have her friends over until at least some things were put away and then I'd rattle them off. No sense in overwhelming her by giving a general "must clean". Be specific so she knows my expectations and let her know the consequences if she didn't finish.