As a working book editor, and writer, I suggest the following:
Powerful evil beings can be depicted as aliens. Much like The Force, it is unknown how they got their powers or what their version of The Force is.
Or they can have super-powers but no need to call them that. They could be natural to them or granted by some obviously unknown artifact, or other non-earthly means.
Have clearly defined good guys and bad guys but go light on the killing.
A just quest by a single hero or group of heroes to stop their town, city or world from being destroyed.
The reader should be able to relate to the good characters in some way. The bad guy or guys, and his minions, are the challenge to be overcome. His powers/weapons or sheer number of attackers have to be dealt with.
Make it fun. Make it noble. And try to avoid lengthy histories. The reader wants to jump into the “present” situation. Look at any hero movie. The basic stories all break down the same: villain does something bad but gets away, first encounter with villain doesn’t go that well, but we learn more about the good guys and the bad guy(s) along the way. The second encounter goes better but serious injury usually occurs. The final encounter is when the hero or heroes launch an attack where everything hangs in the balance. Will they survive? The battle goes back and forth. Then, a certain victory, which may includes the villain dying, escaping to fight another day or not, or being captured or sent to a place where he cannot escape.
The moral aspect is to make sure the behavior of all leaves out the profanity, the sexual situations and gratuitous violence. A hero with principles should practice them, not talk about them. And loved ones. Adding a few or more loved ones is my suggestion.
Clever dialogue and unusual situations need to sound right. To seem plausible in their own world setting. And that takes a little time to do right.