To sign better, form your dominant hand in an open, curved fashion, with your four fingers held together and your thumb sticking up. Motion the hand close to your mouth, then raise it diagonally up a short distance from your head as you close the four fingers into your palm, ending up with a "thumbs up" sign of approval.
Teach your child the better sign in the context of showing them that they have improved in a simple activity or chore. Remember to do this sign with a smiling face and a cheerful voice!
Teach your child this sign as part of the positive reinforcement you show them each time they show small improvements in simple activities or chores, like dressing up or tying their shoelaces.