First I will say I am no expert. I have a 13 year old step daughter who we have 7 days on and 7 days off. I know she treats me different than her Mom, her mom gets the eye rolls and attitude but I don't even though I know she feels like doing that to me since I am strict and lay down the law pretty quickly when I see an attitude I don't like creeping up. I have to think that she treats me better because she knows she will not get away with it at all. First offense is pretty harsh, I ground right away or take away something that really means a lot to her like her laptop.
When I have an issue that I am unable to resolve on my own after trying and trying (like her daily chores not being done) I get my husband (her dad) involved and when Dad is involved you know things have gotten pretty serious so she staightens right up usually.
My husband and I have a 3 year girl and a 18 mos old girl together so I am sure I will be asking the same question in 10 more years, I hear these are real tough years and you would rather deal with the terrible 2's again.
One thing that is guaranteed to work is prayer, get on your knees and ask for wisdom!!!!