Be a parent, not a friend. Clear lines about appropriate and inappropriate behaviors need to be drawn. Remember how you felt when you were a kid. Try viewing the world through your children's eyes. Remember that dads are human and will make mistakes.
Children are very forgiving.
Talk to your children. More importantly, listen to them. Volunteer as a driver or chaperone for children's school field trips. Let children help with household projects. Find family hobbies, things everyone likes to do together.