Be enthusiastic and excited about what you're saying. Grandparents do not have the right to take away a mother's and father's right to do their own parenting. Some necessary lessons only come from struggling through on their own. Discuss discipline with parents and discipline a child only when you are in charge. Strive for consistency between what is permitted by parents and grandparents.
Consistency is one key to effective discipline.
Express your feelings. Let your children and grandchildren see that you have feelings. Laugh when you are happy and cry when you're sad. Help them understand sometimes everyone must hurt a little bit. Share experiences that you've had which at the time seemed completely awful and hopeless but turned out well in the end.