How does one determine right from wrong?

Make a quick, subconscious determination as to whether the consequence in question is important - how will it affect my life, the future, if it will affect the people in my life and how.

If it does not affect others or myself that much, I follow my instinct about whether the action is right or wrong. After that act on it and the results automatically modifies my mentality for future decisions. 

If the consequence in question is likely to be high then I think long and hard about the decision.  I do not make a snap decision in this case (as above), instead I take responsibility and make sure I get information in order to make the best choice. 

Then process the information to determine whether the action will affect the happiness and survival of the people involved, whether it will affect the dynamic of my family, whether it will be against a cultural norm, whether it breaks any laws, whether anyone will be physically harmed and so forth. 

After determining all these factors I weigh the costs against the benefits to those same categories (as well as to myself) and then I will take action. 

I deal with any consequences and then (as above) evaluate the results and let that information guide future decisions.