When it comes to fixing a broken relationship, I have good news and I have bad news. The good news is that no matter how screwed up the relationship is it can be fixed. This will only work, though, if both parties are 100% committed to doing whatever it takes to make it work. Both parties have to understand and accept that it will take time and work and they have to be mature enough to face up to some of their own flaws. If you are both at that place you have an excellent chance of working things out.
The bad news is that if the problems are serious and /or both of you aren't willing to work hard and find a solution, the odds of fixing a broken relationship go down significantly. It's not impossible, but so much more difficult. So step one would be to honestly assess where you and your partner are. Are both of you mature enough to face up to the issues and stick with it long enough to find a solution? If so, go on to step two. If not, ask yourself why you want to save the relationship. People will usually answer that with "I love them" but sometimes that just isn't enough. If you try single handedly to save your relationship, it's very easy to fall into the trap of becoming a door mat to your partner. If they are so selfish that they won't work with you to save the relationship, it's almost a guarantee that they will try to take advantage of all the hard work you are doing.
Step two would be to figure out what is going on. What are the problems and issues that the two of you are dealing with? What needs to be done to fix them? Do the two of you just seem to be drifting apart? If so, why? What has changed? Do you now have kids and find it harder to really connect with each other and care for the kids? Has one of you taken on a new more stress filled job and it's affecting your home life? Once you identify what the issues are you have a much better chance of dealing with them in an effective way. Don't let the clutter of day to day life confuse you. That's not the real problem in most cases. Figure out the real bottom line problems and than work together on a solution. Sometimes finding someone to help you sort it all out can work wonders. Finding a therapist or counselor to help you figure it all out can be a great help. If nothing else, a counselor can act as a sort of referee so the two of you don't get too upset and start fighting. If you do, nothing will ever get worked out. Remember, you can't fix something until you figure out just what is broken and it's no different when you are trying to fixing a broken relationship. If you don't pinpoint what the problem is, you can't fix it so that is the first thing you have to do.