There are many things that parents can do to help instill self-esteem in their child, being a great role-model is one of them. To become a role model to your child the first thing you need to make sure you have is good self-esteem yourself. Children pick up on the body language and the subtle cues that you give out. When you talk to your child they pick up on the subtle cues of how you talk about yourself.
If you talk critically about yourself openly to your children, they will learn to talk critical about themselves as well. Parents are the most important role model their children will ever have, so make sure that you are demonstrating your self-worth in front of your child often so they learn to model your behavior in a positive manner.