Natural consequences or ignore the mild stuff (she doesn't want help from the sitter, then can she do it herself?), invoke consequences for the more serious stuff (It's rude to say that about your dinner. You may eat politely or you get no dessert) and figure out where you are making the situation worse (Does DH read longer when you aren't there? Are you being inconsistent?)
And this...this is the key:
http://www.webmd.com/parenting/guide/parenting-preschoolers-mistakes
"It's easy to hone in on your child's negative actions -- like yelling and screaming -- and ignore the good ones.
Altmann says parents tend to focus on what they don't want their preschoolers to do. "They'll say, 'Don't hit. Don't throw. Don't say 'poopy pants,'" she says.
Fix it: Notice when your child is doing something positive, and reward the good behavior.
The reward for positive actions can be your praise, or it can be giving your child a big hug or kiss. "Those types of things really go a long way with preschoolers," Altmann says.
Tell your child, "I like the way you sat quietly and listened," or "That was good when you were so friendly to the child on the playground.""