What do you do when a friend is taking ad vantage of you?

I do nothing as I understand friend is taking advantage because I created that situtation, so if I do not give advantage friendship relation may be in question. If I should not give any advantage, I should be always careful and will not create such situation that may not be interested to my friend to take advantage from me !!

I try to not let them do it anymore. I just kind of stop contact with them.