I would just relax about it. WIth my kids, I wanted to pick my battles. Our kids had a lot of freedom but we also had a few hard and fast rules. They were allowed to have their rooms as they wanted. One child kept hers Martha Stewart pristine, the other - umm. well not so much.
I didn't want food or wet stuff in there room, but if the room bothered me, I closed the door. If my messy girl wanted help, we would go in the room together and glean and organize. That way she knew how to make her bed, organize her stuff, but whether she kept it that way was up to her.
But if it is really important to you, then you can try taking away their gadgets, X-box, phones, computer until the room is clean.
Both girls are grown now, one is still Martha Stewart pristine, the other one more relaxed but not messy and has a very important job with the Army--so she turned out okay despite the clutter and who knows what else in her room.