We have 4 kids, ages 5 to 13, and have worked with youth at church for many years. We love the "Love and Logic" approach to parenting.
I've asked many parents of grown children the secret to parenting, of course paying closest attention to those who have the best kids. Those with one child often say, "Oh, it's easy, you just have to do , and things work themselves out." But those with many children, seem to always say: "We have no idea. What we tried for the first one didn't work for the second, and what worked for the second didn't work for the third. You just have to love them, and keep trying different things."
That's probably the best parenting advice I've ever gotten.