I have two teens, and I've worked out that I have to actively parent them in order to get them to keep their rooms respectable. I'm quite sure that if I just left them to their own devices, that their rooms would end up a state, and they won't learn appropriate standards or how to keep their rooms tidy.
First of all - no food or drink(bar a water bottle) in their rooms, ever. Non negotiable. If they are ever found to have eaten in their rooms (including sweets etc), they lose their phone privileges. They've both done this once or twice, but now realise that there will be consequences, so don't do it anymore. I really have no idea why anyone would let a child eat in their bedroom, it's really not appropriate, and causes mess and smells, stains etc. IMO it's the biggest cause of unsanitary child's rooms.
Secondly, I clean/hoover their rooms twice a week. In order for me to be able to do this, their rooms need to be broadly tidy - floor clear/surfaces clear, which they are expected to do. I do their rooms on the same day each week so they're in a routine, and I remind them the night before, so they do a quick tidy. While I'm cleaning, I'll pick up the odd thing out of place, i.e. a sock fallen down the side of the bed, or throw away a couple of cotton wool buds left on the dressing table etc. Because I'm in there a couple of times a week, it never gets really messy. If for any reason the children have left their rooms in a state that I can't get in to clean, they have to tidy them, and then clean them themselves. I've enforced this, so now they make sure they are left in a good state for me to clean.
I remind them to bring down their dirty washing before I put the washing on. Mostly they put it in the washing basket (in our room) as they go along, but I ask them to check for any odd items before I do the washing, so dirty washing never builds up in their rooms.
With clean clothes, I put them folded on the end of their bed, and ask them to put them away before they go to bed. I check that they have! They have plenty of wardrobe/drawer space, and we regularly go through and get rid of outgrown/unwanted stuff.
Basically, because I'm in there cleaning twice a week, their rooms never get bad enough that keeping on top of them is a problem. In between cleans, I don't force them to make beds etc, and I don't go looking in their drawers etc unless they are clearly a problem (e.g not shutting properly etc), it's just a basic level of tidiness, clear floors, clean surfaces that I'm looking for. If I wasn't going in there twice a week, I'm sure that mess would gradually build up, though.