Hey - being new to the board, I'm not sure how old DD is but my DD is 16 and my DS is 4.  They both have the same 'my space is ALL space' concept, so they are inclined to leave stuff all over.

So, we have rules... for the teen, she has to keep her floor 'fire safety' clear, which means a clear path to the door and windows.  Also, no food/beverages and no candles.  Sounds obvious but turns out, it wasn't! 

Also, she does her own laundry but after she was wasting much time getting ready in the mornings because she couldn't figure out what was clean/dirty, we insisted that she clearly separate them.  I have a basket that is for her stuff to get collected into each day from the rest of the house (kitchen, den and living room) and she takes care of it each night, bringing the empty basket down before bed.   Non-compliance could mean a loss of computer/internet time, cell phone or - if things get completely out of control - I stop being her 'chauffeur" for the day! 

For the 4 year old, we have bins & baskets (labeled with words and pictures) for storing toys and stuff and things get put away before bedtime.  We encourage some toys to be tossed into their containers and "Yay! Score!" stuff with high fives.    Whatever he doesn't pick up, I put in a big box and he loses the stuff for the night and next day.  He's figured this out faster than the teen... 

Good luck!

- Ann -