The right sort of sun: middle-aged, middle-sized, with middle of the range radiation.
The right distance from the sun: not too hot, not too cold.
The right size: just enough gravity to retain a respectable atmosphere.
The right sort of rotation: not too fast, not too slow and tilted just enough on it’s axis to produce well-defined seasons.
Plenty of the right materials: lots of water, and enough carbon, oxygen, nitrogen and hydrogen plus small amounts of other elements.
Freedom from the wrong materials: heavy metals and radioactive elements are not very plentiful and are safely locked away in mineral deposits (until people dig them up…)
The right kind of sea: providing a reservoir of water to evaporate and fall as rain, storing heat during summer for release in winter, keeping the composition of the air just right, and more.
The right kind of atmosphere: just enough carbon dioxide to keep plants alive but not so much that we couldn’t breathe, just enough oxygen so we can breathe but not so much that fire would be impossible to control, just enough air so that the sun can still penetrate.
– Adapted from “God Is” by Alan Hayward