You could possibly try my "teaching" trick. I always start any messy activity with a "tidy up plan warning" Like " we'll play with the toys now BUT if we want to go play outside we'll have to tidy up" and at home when nannying I used to say " if you tidy up while I do dinner prep then we can all go to the park for a while. If I have to help you pack up you'll have to hang in the kitchen while I prep dinner and there won't be time for the park.........." The other thing I did was to use behaviour patterning. If the kids got a new toy or tried a new way of using an old toy I'd help them tidy the first few times and add this help to the above two suggestions. I also model tidying up myself by telling kids what tidying I'm doing and why. "I need to tidy the toys in the living room so we know we haven't lost any bits and so I can vacuum"
This was effective.
So I guess my ideas are
1. give a warning of clean up expectations before the activity starts
2. tie tidying up to a positive "extra" instead of a negetive "take away"
3. pattern the behaviour you'd like to have them continue.
4. explain the importance of tidying and model tidying up

Good luck! Having been a kinda teacher I can tell you every little person is different and they all have a different leel of what they think is "tidy"!