how do I get my 6 yr old to follow rules

My 6 yr old daughter seems to act out literally the moment we turn our back.  (Like if I go to the bathroom or do chores).  She will sneak food even though she's not allowed in the refrigerator or cabinets.  Annoy her brother until he screams.  She will open doors and go outside if she thinks she won't get caught.  She has taken the keys to my car and tried driving to the store but couldn't get the car started.  She sneaks her friend in the house while we're sleeping.  She plays ball in the house and jumps on the beds multiple times a day knowing she's shouldn't.  Time outs and revoked privileges don't phase her.  She follows me threw out the house continuously talking about random things that don't make sense.  I take her to the park to play and she overwhelms the kids with her constant rambling.  We talk about expected behaviors prior to going in a store but the minute we walk in the door she starts running, jumping, yelling.  She does well in school, learns very easily, is friendly, but gets written up for talking a lot at inappropriate times.  She almost got kicked out of her school play for talking too much.  I asked my doctor for parenting advice and his suggestion was neurological testing to find the right meds.  Her diet is mostly fruits and veggies.  No sugar, sodas, and very little processed foods.  All I want to know is how to help my child listen and follow rules.  

[Kevin Kennedy, Ph.D.]

The doctor is likely suspecting that your daughter displays ADHD, and that is possible but does not explain all her behavior. While neurological evaluation is not necessary, I would recommend an evaluation by a pediatric mental health/behavioral health clincian because her behavior is outside the norm for childhood behavior problems (even for children who display ADHD). In addition, you need help with managing behavior. I suggest you read (carefully) Lynn Clark's book SOS Help for Parents and follow his guidelines very specifically. You'll be glad you did (see www.sosprograms.com).