Saving a relationship can mean different things.
 First, your partner (spouse or lover) might have already left you and you may be trying to get him / her back.
Or second, your relationship might be faltering and about to end, but you have not separated yet.
These differences do not matter when it comes to the question of how to save a relationship.
Even if you have already broken up or about to break up - the reasons do not differ.
 And when reasons for a breakup do not differ, the ways to get your ex back do not differ too.
How to save a relationship, then? First of all you need to understand the most fundamental law of human behavior: "People desire what they can not have".
This applies for relationships too, and in the case of your ex, this becomes "The easier someone is for you to get, the less you will want him or her".
In matters of saving a failing relationship, this means the world.
If your partner has left you or is about to leave you, you need to get over the begging and crying period immediately and get on with straightening your life.
Not only this is crucial for you to continue a normal life, it is also crucial on how to save a relationship.
After you have stopped calling / text messaging / begging etc.
your ex partner and have straightened your life, it is time to put everything in perspective and think about the roots of what made your relationship fail.
This step needs to be done after you have eased up a bit because otherwise it is impossible to weigh the reasons of the failing relationship.
 And when you can not assess those reasons easily, it will be harder you to save your relationship.
A full guide on how to save a relationship might actually work because we are all humans and will respond similarly to similar actions.
 So a previously tested / proved guide of getting your ex back can work wonders if followed correctly.
It has worked for tens of thousands of people and there's no reason it should not work for you.