I'm a member of www.FLYlady.com, which really helps me keep my house clean and keep routines and have a healthy attitude towards it all. It's geared towards adults getting their homes and lives in order, but she provides a "control journal" for children to keep track of their homework, chores, etc, on their own without their parents nagging, which might really help. Kids (and husbands!) automatically resist us when we're telling them what to do, even if it's for their own good. The student control journal helps them stay organized and establish routines. Here's the link to the control journal: http://www.flylady.net/images/student_CJ.pdf#search=%22st...
Also check out her homepage flylady.net Her systems might really help you find peace in your own life like it did for me.
Flylady is an advocate of her colleague's website, www.housefairy.org, which is a website to help motivate and encourage children to clean their rooms. On the website there's a video of The Housefairy where she talks to your kids and tells them she's going to stop by unexpectedly every once in awhile and check on their rooms and see if they've been cleaning it like their parents have asked and leave little notes and rewards if they have. The website also helps give you ideas on how to make a game out of cleaning, and turn it into a positive experience so they can develop good habits for life. Praise and rewards are usually bigger incentives than punishment, and much more positive and help their self-esteem. In fact, while studying for his Master's in Business, my husband learned that people performed better with the incentive of receiving recognition and praise than they did with the motivation of monetary rewards in the workplace. You can plan family activities as rewards, doing what she wants, which she most likely prefers over material things, plus it sends a better message. The housefairy.org website has a LONG list of incentive ideas, posted by other parents.
Good luck! Be firm and make sure there are consequences, both positive and negative, for their behavior. Consistency pays off. I am a BIG advocate of the Love and Logic parenting style of letting your children suffer the natural consequences of their choices and enforcing limits, but doing so in a loving, empathetic way. Love and Logic also stresses the importance of reinforcing a warm parent/child relationship by being involved and spending time together. They offer awesome parenting classes that I strongly encourage taking (www.keriparentcoach.com is their excellent local instructor here in AZ), have some great books ("Parenting with Love and Logic"), and DVDs and CDs. Check them out at the library or purchase at www.loveandlogic.com When I attended the parenting classes it became apparent that this approach to parenting is very similar to how I was raised, and I really appreciate my upbringing and always had a fantastic relationship with my mom, even during my teenage years. My mom recommends "The Parents Handbook," by Don Dinkmeyer, also known as the Systematic Training for Effective Parenting (STEP) Handbook. Also, "For the Love of Children" is great.