Getting Kids to Clean Their Bedrooms (Without Nagging!)
Sit down at a calm time and agree on some standards. Then, when necessary, give your child a warning when her room doesn't meet the agreed-upon terms of "cleanliness." Allow enough time for her to clean the room without too much pressure from you, but still in a reasonable amount of time, from your perspective.
Warn her of the consequences if she doesn't clean up: Tell her that you will come through her room with a box, into which you will place all the things she didn't put away. Tell her that the box gets a three-day time-out the first time she doesn't clean up in time, a week the second time and two weeks the third time, with the box being donated to charity the fourth time. If this comes to pass, calmly tell her you're sorry she chose to break your agreements, but that to be a consistent and trusting parent you need to do what you both agreed to do if she didn't clean up in time.