Make it a game! Put a chart in her room with star stickers. Every time she gets through a successful week of cleaning, reward her with a trip to the store or baking brownies together. Sing a song that encourages the clean-up routine. Help her and lead by example. If your room is dirty, you'll be hard pressed to get her to clean hers! Get excited when you accomplish a cleaning task, and you'll notice her excitement when she finishes one too. Let her help you clean other parts of the house, and praise her on it as much as possible. Turn on some good music and boogie down while you clean. Dance and sing into the hairbrush before you put it where it goes. Giggle over the tower of blocks before it's ripped down and put up. Start a stuffed animal train by throwing her one and having her throw it in the pile. Praise her good catches and throws.
Also, help her showcase her favorite items!
Whatever you do, don't turn it into a fight and don't expect her to perfect it on her own. Cleaning is a skill that is learned, not one that we are born with. It's a process. If she's having a hard time figuring it out, teach her.
Make sure she has specific places to put things, and label places for clothing, books, stuffed animals, and toys if you must.
Supply plenty of baskets and shelves to put things on and give her one 'anything' bin for all the odds and ends that don't have a specific place!
And every now and then, go all out and clean her room for her! Show her how great it is to have a clean room, how easy it is to find things, and how much more fun it is to have room to spread out on the floor.