Try to find something good in every day, whether it is a good coworker, an interesting customer, etc. Ask customers more than just "how was your day" but "what's a great book/movie/etc that you have recently read/seen/etc." or just try to be nice. At the end of the day, find a way to get away from work. Do that things that don't let it become your sole purpose in life. It's just a job, not you.