Deity Design Guide (5e Guideline)
From D&D Wiki
5e Deity Creation
While there hasn't been much advice or direction from core material, there are still some things that should be considered when creating a deity. The topics below are to help think of ways to bring a deity to life.
A brief description of how or what the deity looks like, any gear your deity might wear or weapons it is wielding, behaviors like a twitch, soft spoken, anxious and quick moving, interests, any nicknames the deity may have, and the holy symbol for your deity
Deities are aware of other deities and not all of them get along. On the other hand, a deity might have friends or alliances for the day its enemies come after it.
Describing what believers of a deity do for their god is helpful in explaining how to bring honor to the god. Do they build temples? Perform rituals? Pray once a day, twice a day, or at all? Are sacrifices made to the deity and what are they if so?
In the event there are temple for your deity, what details would one expect to see? Is the deity’s symbol on the front of a building, or on top of it? Are gems covering the temple? Does a temple require a size to it? Does your temple need to hidden? How would it be hidden? Do temples exist on other planes?
How did your deity get its divinity? Was there a power struggle with another deity? Did it perform many favors gaining demigod status and work its way higher? Was your deity created as a lesser deity?
Does your deity have any goals or find itself content with its position of divinity? If you give your deity goals, try to give details about that goal instead of being vague. Why would a deity want a legendary sword? How about the name of the sword, and why it is important. How would an artifact be significant to your deity? Are the enemies also meant to be a goal? Has your deity given thoughts to how it would carry out the elimination of competition?