Well, the first step is "try not to be jealous" - which is a big step, and really hard, and it took me a long time to get there, but it's important. Other people's accomplishment and skills do not diminish your own. Wherever you are in your artistic development, you should be proud of yourself. You're making things! That's a hell of a lot more than most people ever do!
And I do try to use other people's art as inspiration to improve - I find something I really like, and I go "man, I wanna be able to do that!"
... At the same time, though, I make sure to never, ever compare myself to them. Looking to others for inspiration is okay, but do not look to others to be your measuring stick. The only person you're trying to compete with is yourself. Keep your old sketchbooks around, flip through them when you're feeling down about your artistic progress, and compare where you are now with where you were years ago. I can guarantee you, you're nearly always going to be better now.
And that's really the only goal you're supposed to have.