We've touched on this on other days, but it's incredibly important to surround yourself with not just good couples, but Godly couples. Couple who know and understand the relationship God wants us to have together.
I am always reminded of the movie with Kirstie Alley and Tim Allen called For Richer or Poorer where they are forced into an Amish community in hiding. Before they go there, they have a horrible marriage and are surrounded by selfish friends who encourage them to be selfish too. When they are surrounded by strong people who encourage selflessness, they begin to change how they see each other. The movie is a little silly, but you get the idea. I've seen horrible advice given on Facebook especially to wives that encouraged thoughtless and selfish acts of retaliation to husbands. Look at many of the celebrity relationships, people with open marriages who allow their spouses to have relationships with other people. It is so easy to go, "well, if they do it, I can do it too!" We look to other people to justify our actions even when we know they are wrong. Don't have friends who encourage your own selfish behavior and thoughts, it will only help destroy instead of help build up. Have friends who will tell you when you are being selfish, or are acting in ways that are unbiblical or downright wrong. Of course, this requires being OK with being held accountable, but it is definitely better than the alternative.
Sometimes, when we are lost, we just don't know the right direction to take. Other Godly couples can be helpful in that, too. Being a part of a marriage ministry where you can take classes and go on retreats that encourage Godly marriages can be lifesaving in a marriage. Just think - bad influences are stronger sometimes than good ones, so don't even give bad influences a chance.
There might also come a time when your marriage becomes one to model others after - you just never know when your experiences could help save another marriage.