I don't often feel taken advantage of because:
----I'm pretty good at saying no when i don't want to do something.
---When i give i do not expect something in return.
---When i do expect something, i communicate it clearly before hand.
---I know what i am about: my core/purpose/etc.
---I give people a chance, but i know there will always be some who disappoint me, and i'll simply move them out of my life. I trust in stages knowing this is the case.
This prevents many problems.