A lot of good science fiction has been generated from this question. Larry Niven is highly recommended in this area, and I'm sure others here have their own recommendations.

Human moral codes derive, at their basis, from how human beings live and survive. If the alien species is a "Star Trek" type alien--basically a human being in a funny mask--similar moral basics would apply.

However, the idea of "individual rights" would be nonsense to a hive mind. A sessile or plant species that did not need to alter its environment or engage in productive activity to survive might have a different idea about property and ownership.

A predator species may have no conception at all of "live and let live." The human species is intelligence grafted onto a carnivorous primate--like the panda's thumb, kind of a kludge--and we tilt in both directions. One Star Trek episode postulated parallel universes, one where the Federation lives by the Prime Directive, the other where the Federation has conquered the known galaxy. Same species, tilted two ways.

It's interesting that in the first universe, the Federation is constantly having to battle to the death with species who are less fussy about their ethics. Does the "bearded Spock" imperialist Federation have that problem? Might make a good story.

"That's all it takes; one simple decision. We are not going to kill...today."

- James T. Kirk