This is a small quick-easy idea basket to give some ideas to create a prime world as long we consider every plant is a prime world. They can also serve for various other things as well, if you have something more I'll add it.
Stellar objects types :
Planets : No explanations required I think.
Asteroids : Are small, usually composed of rocks, metals and ice, they can exists in so called belts orbiting around a planet or in fields somewhere in space, or just wander alone.
Gas giants : Are large planets that is aren't primarily composed of rock or other solid matter. This means that usaly most of the action will happen in thier moons, though in a multiverse of magic everything is possible, as these planets could be for example direct reflects of one particular element.
Moons : Are orbiting around worlds, they make good places for isolated events, secrets etc... In an esoteric point of view, they are commonly associated with magic, femininity, cycles (time, death, tides etc...), psyche (twisted behaviors, lunatism).
World types :
Planar worlds : These worlds are strongly influenced by one of the inner our outer planes at the point of looking like them. They basically look like the plane they are influenced by, its denizens are far more common. The influence can be seen at various degree, sometimes there are only few hints a prime world is suddenly changing to become a demon world or a fire element world.
Sand / Barren.
Ice / Frozen.
Rocky.
Crystal.
Volcanic : This world is young and still has a lot of volcanic ability.
Metallic : Crafted by someone or naturally grown, most of this world is composed by a certain type of metal.
Dead world : There's nothing but ashes and dust here. They can be imbued with negative energy as well.
Oceanic : The world does have few above sea landmasses and most of its life lies beyond, in the seas.
Jungles/Forest : The world is covered by extensive plant life-forms.
Earth-like : Like our world.
Swampy : On these world, earth and aquatic life are mixed at the point its impossible to make a clear distinction between both.
Crafted worlds : These worlds aren't naturally born, but crafted by someone or something, they can be of various forms.
Special features :
Floating islands : For some reasons, the planet does have floating island, or is composed of floating island within its atmosphere. (Very reminiscent in Japanese creations)
Dual worlds : At some point two worlds have met and exist close to each other without crashing at the point that traveling , communicating or fighting between them is quite easy.
Shadow planets : Sometimes the planes of shadows extend to the reality to cover an entire planet, these planets are hardly visible from space.
Living planets / Sentient worlds : The planet is self conscious and is a living organism. (Those who have played Alpha Centuary should get the idea).
Populations :
Sentient machines.
Insectoïd / hive-mind races.
Crystal lifeforms.
Home of one common fantasy races.
Ruled by dragons / may be battling lesser races for example.
Place where an old powerful race is imprisoned / hidden.
Undead unlife-forms.
Parasitic life-forms.
Zombie/Infected life-forms.
Aquatic or Earth life-forms are absent.
Non-organic life-forms.
Invisible creatures.
Gods/Titans walking the land.
Setting :
Common fantasy world : You know enough about these.
Post-apocalyptic.
Devastated world with hidden remains.
Prison world : can be of one very powerful creature or just a random prison.
Monastery / Sanctuary.
Lifetime season ecosystem (the planet orbit is very very slow).
Two empires battling each other.
More advanced begins ruling/watching over credulous natives.
