Give your child self confidence. Don't let a chance go by to praise him, but only when it is deserved. Kids are smart, they will know if you are making a big deal over nothing. Don't give your child unrealistic standards. If your child makes average grades, even though he studies hard, don't run him down about it.
Most people are average, and every child has talents that can be encouraged.
Don't give him an ulcer over something that he just can't do. Finally, choose your battles. Don't freak out over every little thing. Most things won't matter in a hundred years anyway, so stick to the basics.