It's not a clear cut thing. There is lots of ambiguity in life. Often I won't know it's the right thing until after I do it.
But when i do the right thing, I get a feeling within that I have indeed done the right thing.
It's hard to describe.
I don't convince myself to do the right thing. If I have to do that then it is probably the wrong thing :-)
What makes me feel good, what make me feel right, is helping people. The action itself is the reward. That's what makes me feel that it is right.
I'm sorry. I can't articulate it better right now. I think if you are being true to your nature, the things that are true to your nature come easily to you. They are effortless. And in that space the world just feels right to you.
I probably need beer before I can really explain it ;-)
I understand what you're saying, but we should remember that (for example) Germans who helped murder Jews, gypsies, homosexuals and mentally retarded people also had “warm fuzzy feelings” fostered by a daily, unrelenting diet of government-sanctioned “information” and social approval that convinced them that they were doing “the right thing” to help others and make the Third Reich strong.
Vague “feelings” are comforting, but they can easily mislead. Study of moral literature (especially the Bible), unremitting introspection, and constant questioning of one's motives are ways to strengthen one's sense of ethics.