The most important part of being happy with what you have is recognizing that Hashem has decided that you should have exactly what you have now. Anything more or anything less would not only not be good for you, it would be bad for you. Hashem has given you everything you need in this world, monetarily, mentally, etc.
teen, simply think once a day “Everything I have is a gift from Hashem”. A good time to think this would be by “posaech es yadecha u’masbea lichul chai rutzoin” in Ashrei.