Let your children know you believe in them. It means a lot for them to know that you support and encourage them. They will be able to dismiss their fears and self-doubt if you believe in their capabilities. Help them discover their strengths and let them know how great they are doing.
It is also important to show interest in your child's interests even if they differ from yours. By doing so, you also build your relationship with your child which is very important in increasing motivation for kids.