I would advise them, above all, to constantly tell their kids how much they love them, regardless of what is going on. To teach them to say "please" and "thank you" as soon as they can talk. To never verbally put them down, and to be diplomatic when they do make a mistake. If they fail a test or lose a ball game, to hug them and give them encouragement.
I had my kids very young, and I had no idea what I was doing. But I loved them. I do see a trend where I have heard parents say, "I'm going to raise my kids the opposite of the way I was raised!" That is so sad, because it means they resent their parents. On the up side, I think, from generation to generation, when raising a child, the parent tends to avoid anything negative their parents did or said to them when THEY were being raised. But, trust me, parents are human, and they do make mistakes. However, valuable lessons are learned.
I hope this makes sense!