Your dog should learn to associate different kinds of rewards or appraisal with certain behaviors that you want her to repeat. It is important that you repeat any action so as the dog associates a behavior with a reward at all times.
Example: Take a cookie in your hand hold it in front of the dog and start moving it up and behind her face until you lead her to sit down as she cannot follow the cookie anymore. As soon as the dog sits you say sit and appraise her, Good Dog, and then give her the cookie. The dog will associate the appraisal and the cookie with sitting. The desired result would be after a lot of repetition; the dog connects the above mentioned actions with sitting and reaches a point where she reacts only to the word sit, thinking that the rewarding will follow. After that the dog reaches a point where she can obey to the word no matter who gives it. This means that another member of your family can make her sit, just by saying the word wherever the dog is (during her walk, or in the house etc). In order for her to maintain the desired behavior you should repeat it many times, even under various circumstances and in different places, so as the dog performs in the expected way at all times (at least 9 out of 10).