How do you teach “Tidy Up”?

I emptied Maisy's toy box and together we filled it back up one by one. Firstly I put the toy 'In the box', showed her how, guided her, then a treat when she did it. Her aim wasn't great at first but she got a treat for each effort. Now when we play 'In the box' she takes things out of the box just so she can put them back for a treat. Sneaky.