As I have learned, trying to get my daughter (who turned 6 on Thanksgiving) to clean her room is one battle I am sure to lose every time. First the no's....then the crying....then the speech about how her room is too big or how under her bed scares her. After yelling, time outs, and loss of privileges....I learned that maybe cleaning her room all at once may be a bit overwhelming to her. For her, her room seems to be double the size that I see it, with twice as many toys.
Instead of telling her to go clean her room...I divide it up into smaller projects throughout the day. That way she doesn't see it as cleaning, but helping Mom out real quick and getting a high five!
I usually start with her clothes. She is notorious for leaving clothes on the floor! I'll ask her to just put her clothes in the hamper. When she's finished...she goes back to playing. After an hour or so, I tell her she'll have more room to play if she put her books away. "That's a great idea Mom!" Later in the day when she starts winding down....we split her toys into two parts. First she picks up one half of the room, and then after her bath she takes care of the other.
It may be an all day affair, but she does it by herself and without whining!