Set them up to succeed.  Make it easy for them.  Then encourage them to put things away.  I believe in a labeled playroom and a place for everything that is clearly marked in some way.  When they were young I woudl take pictures of their things and tape it to bins in their playroom.  Now I do it with words only.  They are pretty good about it.  In their bedrooms they help with putting laundry away to help them remember where to find everything and where everything belongs.  They have baskets on their dressers for silly bands, chains, watches etc.