I think the secret is never expect anything back... then you don't get disappointed. Assume that anything you do for someone else won't be reciprocated, so you only give stuff away because you want to get rid of it and they have a need for it, not because you want a thank you. Similarly, if you do something for someone else, don't expect a fuss, just do it because you want to (and can do it) and leave it at that.
I believe that what goes around, comes around, so all your good deeds will be rewarded in some way, one day, just not in ways you might expect.