Some people have a tendency to get confused about things like morals, ethics, good or evil, right or wrong, or at least act the part of being confused, whereas for the most part, whether something is good or evil, is fairly straightforward, and implicitly recognizable. One way to recognize the difference between the two is simply to imagine yourself either in the other person's shoes of a given situation, or to imagine if everyone else in the world did the same sort of thing as you are currently contemplating doing, which will often provide the much needed perspective as to whether the deed is right or wrong.
That is to say, if you believe it's fine to lie to someone, especially about something that is of real material importance, but then, unbeknownst to you, they were to do the same thing to you, in all probability, you would not appreciate the fact that they lied to you and thereby took advantage of you, so the only reasonable conclusion to recognize, is that lying is not something that should be done, and thereby we should do our part not to participate in being a willful player in the lying game.
On the other hand, let us say that we do generous acts for other people, expecting absolutely nothing in return, perhaps because it makes us feel good for having done so, or perhaps because we want to do our part to help other people, that need such help, so that, if other people, were to have the same sort of outlook, this would obviously add to more generous acts being conducted one to another, and hence leading to a more generous world, therefore a better world for our generosity, which is good.
This so indicates that when we deliberately throw trash on the ground, cheat on our tests, steal small and trivial things, or change stories in such a manner that we are made to look better than we really are, that none of these things, repeated by others at the same scale, is going to actually make our society better, even though each of these actions, are relatively speaking, fairly minor. So then, we ought not to do those things, if we truly believe that none of these things are actually contributing to making the world better, for one another, and since we cannot control the actions of another, but can control our own actions, through self-discipline, then we should control our actions, and thereby lead by example to others.
The deeds and actions that we do should be consistent to what we truly desire that we would receive from others in our interactions with them, so that, if our preference is to deal with those that are honest, fair-minded, and courteous, that should be the way that we conduct ourselves, for thereby, that would be consistent, as opposed to believing that it's okay, for us to lie, cheat, and deceive, from time-to-time, but it isn't okay for anyone else to do that when it benefits them, at our expense, from time-to-time.
Great societies and healthy relationships are built around positive qualities, of which, these attributes are equally available for all to utilize, if only, we would more often and consistently do the very things ourselves that we wish that others would do in their interactions with us.