We used to have a rule that if the kids left toys anywhere in the lounge on a Sunday eve, they would go up in the loft for a while.
Result: Lots of items in loft, kids did tidy up a little, but mostly they raged at anyone who left anything out (each other or their own friends). They didn't want to tidy up after themselves, each other or their friends. The tidy-up-or-in-loft-rule led to lots of arguments between themselves and with any visiting children.
Someone other day said that she warns her DC to tidy their rooms, anything left on the floor when she comes into vacuum into the loft. Sounded a great idea, they do tidy up she says... but then I remember what a failure this was (for us) in the lounge, in the past. I can hear the complaints already "I didn't get that out!! It was [DS2 name]! He should tidy it up!" (even though DS2 might deny touching the items, the items are not in DS2's room, sigh).
So, er, how do I get past this one?