I start by not having a lot of stuff in their room.
The toys are in the living room. So 1. They aren't playing unsupervised (and thus don't have the freedom to let impulses run free like I did when I was 5 and tried to clue the bed to the floor with toothpaste and tinkerbell powder

) and 2. The mess in the living room is more immediate and obvious that it needs to be tidied up so the rest of the family can enjoy the space too, and 3. There just isn't much in their room to strew around.
As it stands currently, about every third day I have them all scoot under the beds to pull out books that have been dropped, and random lonely socks, etc. They think it's fun, the stuff gets pulled out and put away, and they take care of the dustbunnies.

Other than that, there's really no cleanup to be done. They make their beds in the morning, and I require them to drop laundry *in the laundry basket*. If they get lax about any of it, that's my signal that they need more supervision and reminders from me for a while.