I think there are two fundamental questions: Is there such thing as right and wrong? And if so, how does one know what is right and what is wrong?
A commenter below says right and wrong are only human constructs, but that raises the question of "which humans?" Arthur Leff calls this the "grand sez who?" Is right and wrong a preference, as I might prefer meat to cheese? If so, then who's to say my preferences are more or less valid than anyone else's?
Most people act as if there is a right and wrong beyond preference. Public discourse is full of criticism of "wrong" behaviors and attitudes. Is it wrong to be racist (for example)? Is it wrong to dislike cheese? Are those two different? Why?
I think they are different, and I'd bet most people do, too. If right and wrong are merely human preferences, then no one's "right" is better than my "right." If right and wrong is a human construct we're just arguing about which cheese tastes better.
But I do believe that right and wrong exist, and I believe that God determines what is right and wrong. My motivation to do right and avoid wrong (not that I do it well) is to please God. I'd like to be the kind of man that pleases God. And that's enough for me.
To answer your original questions - the fundamental moral tenets of all the great world religions are pretty much the same (not to say all religions are the same or equally true, but the moral teachings are the same). Follow them.
Do it because it's right, and you're a person who does the right thing. You're not a loser if you're pleasing God.
Good luck to you!