I think the principle that any volitional act that is good for self and/or society is moral, and any volitional act that is bad for self and/or society is immoral is enough. If that was the only guiding rule, it should be extremely easy to teach. Even small children can comprehend that without wasting hours and hours at church or the Kingdumb Hell.
Within that, most of the work is finding out what is good and what is bad. Trial and error are permitted, and voluntary acceptance of risks is necessary if society is to move ahead. However, if this were practiced universally, society would be far ahead of where it is now--notably, I believe Nimrod attempted to preach and teach this very simple belief, and was confused for doing it by that Almighty Lowlife Scumbag Jehovah.