Anyone who owns a dog, regardless of the breed, one of the first things you teach it is to sit.
For Sadie, Dad would say the word while pushing gently on her behind to get used to the word and action. Later Sadie learned to sit by the word only and without any human assistance.
Once she could sit on her own we would reward her with liver treats. Then that's were we tried the hand signal. The hand signal is were you have a liver treat or any other small treat in your hand, make a fist, allow the dog to smell the food in your hand, then draw your hand to your shoulder. With repetition and patience, you will never say the word "sit" again.