Communicate. If you're happy about something, speak up. If something is bothering you, speak up. Don't expect your spouse to be a mind reader. Share your own thoughts and feelings and viewpoints in a non-confrontational manner.
Love each other. Physically, yes; but emotionally, too. Always keep in mind what it was that brought the two of you together. Hang on to it. Whatever happens, remember that you're in it together. Stay supportive of each other. A problem shared is a problem halved.
Be positive. Don't let the turkeys get you down. Remember that the glass is half full - not half empty. Look forward, not back. Remember the good things, discard the bad. Learn from your mistakes, but don't dwell on them.
Be your own family. Don't allow either set of parental in-laws to call the shots. Love them all, but keep them at a distance. And make sure that you divide your time evenly between them all - assuming that they're not totally dysfunctional people who should be avoided at all costs.
Put up with each other. This last tip needs a little bit of explanation. When my wife and I got married, we took our vows both in English and in Hungarian (her ethnic heritage). I asked the minister of her Hungarian church to translate the vows I would be taking because I wanted to know exactly what I would be agreeing to. Well, they had the whole "love, honor and cherish" language, but there was an extra little bit. We both agreed to "put up with" each other. - That was the literal translation, "to put up with." My wife and I were both struck with the honesty and integrity of that language. As to the vow itself: the Hungarian version wasn't the typical "I do", it was "so help me God, I will try to do this." We both loved the leeway inherent in that statement. We were agreeing to give it our best shot, and as long as we did that, we were being true to our vows. And, from time to time, one of us (out of the blue) will say, "Thanks for putting up with me," to which the other always replies, "Thanks for putting with me, too." - We're currently at 36 years and counting.