There's an old joke that "the secret to a happy marriage remains a secret", but I like to think that's not exactly true.
I was single for a very long time, and made a lot of mistakes along the way. So my advice is based on the idea that you can learn from the things I did wrong.
What I'd suggest first is to be very, very careful about the people you associate with. If you want to be married to a decent, respectable person, then hang around decent, respectable people. Relatively speaking, there are saints among the sinners, and sinners among the saints, but that's not the way to bet your life. I used to know a guy who spent all his time in bars, and wondered why he couldn't meet any decent girls. No wonder he was divorced *twice *before the age of 27!
The second thing is to be really sure about what you want--and make sure that whoever you're considering spending your life is just as confident. "Finding yourself" after marriage is one "heck" of a lot harder than doing it before strolling down the aisle.
Also, I've found that similar value systems will help two people get along a lot better than mere physical attraction or even common hobbies. (For example, two people may both play a lot of golf--but the person who plays for relaxation will be miserable with the person who has to win every single time.)
Finally, the faith that two people share is probably going to be the foundation that supports them when all else fails (and trust me, life will throw you wicked curve balls that you will swing at and miss again and again). Better make sure you're both grounded in something that can see you through.
Oh, wait, one more thing...be patient. If you want to get married in the worst way...you will.