Sometimes the basis for good advice is bad mistakes. Other times you can give good advice because you've lucked out and done it right.
I've made a lot of mistakes in my life so far. But one of the best decisions I've ever made was to marry my high school sweetheart. Darlene and I met when she was 15 and I was 16, and we dated for six years before we were married. We got to know each other very well (in every way except one!) and became best friends. We saved sex for the night we were married, even though that was not an easy thing to do at all.
I'm all in favor of long courtships, although it doesn't mean whirlwind romances can't work. However, I do think you are pushing your luck if try to have an engagement longer than 6 months. (Ours was 18 months, and believe me, that was WAY too long.)
I also think marriage counseling is a good thing, though the counseling we got wasn't all that great. (I think our pastor missed that class in seminary -- all he said was, "Take her to the Ice Capades." We've been married almost 21 years now and we still haven't been to the Ice Capades.)
Darlene and I are very different in our personalities. That has made for a stronger marriage, I believe. Our areas of strength and weakness complement each other. As a result, we have learned to listen to, respect, and depend on one another.
Both people in a marriage have to work at it to keep it strong, just as you have to work at maintaining a friendship, only more so. You have to set aside time to be with your spouse, to make sure you are always communicating and listening.
Most of all, of course, we love each other. We've discovered that love is not just a mushy feeling, but an utter commitment. Divorce, like suicide or murder, should be unthinkable. One reason our society is so full of pain and brokenness is that divorce, like murdering an unborn child, has become "a choice."
The Bible gives the best advice of all about marriage: Husbands, love your wives. Wives, respect your husbands. Leave your parents and cleave to one another. Honor your spouse like you would honor your own body. Be faithful and submit to one another.