I recall reading that one of the best predictors of reported happiness is how much a person tends to compare herself to others. (I'm fairly sure I got that from the book "The How of Happiness" by Sonja Lyubomirsky)

You can probably get a quick but decent estimate of where you are on that "comparison-tendency" scale by recalling if you ever feel a sting of jealousy or if it otherwise negatively impacts your mood, or initiates a mental comparison when you see that someone else is up to something really amazingly cool on facebook. How do you generally tend to feel when you see people who are better looking or richer, or <insert desirable characteristic that others have and you don't> ?

I compared myself a lot with others some years ago, but all it took for me to get rid of that nasty mind-habit was to become aware of it every time I was doing it, and realizing that its a stupid and unhealthy habit. Thinking back it probably took me somewhere between 4 and 6 months until this way of thinking became essentially extinct and ultimately even somewhat alien. And I'm happy to say that I'm much happier now, arguably in part because I kicked that habit of thought.

So if you're suffering from this bad habit as well, the way I got rid of it was by simply realizing that it's bad, noticing it when I was doing it and simply moving on. Over time the frequency decreased on its own. The happiest people apparently hardly even know what exactly is meant by "comparing themselves to someone else". Seeing someone who does better than them in any desirable area simply does not trigger any kind of negative emotions, or feelings of inadequacy whatsoever. The opposite in fact, they tend to feel glad for people who are doing well, even if those people are doing better than oneself is.