We overestimate the misery we will experience after a romantic breakup, failure to get a promotion, or even contracting an illness. We also overestimate the pleasure we will get from buying a nice car, getting a promotion, or moving to a lovely coastal city. So: lower your expectations about the pleasure you'll get from such expenditures.

I found this useful for updating my views on what conditions are conducive to happiness: http://www.ted.com/talks/dan_gilbert_asks_why_are_we_happy/transcript