Have a place for everything and everything labelled with the words and a picture.
Get her into a routine of putting away what she was playing with before getting something else out.
Get both of you (sorry!) into a routine where you tidy up at the end of the day. Perhaps put some music on to make it seem more fun.
When she's older and has learnt how to tidy properly, she'll be able to do it on her own.
I've found that if you do this sort of thing early enough, it pays dividends later on.