Depends on your notion of divinity. My campaign has two forms: "gods" and "spirits."
Gods are living creatures whose life-essences have become tied to a (demi)plane. The god's power is tied to the size of his realm. Most gods know how to do it but don't share and even if you do know how to do it, you have to find an unclaimed plane. Taking a claimed plane is virtually impossible for mortals since the gods' plane, to some effect, *is* the god. Killing them on their home realm is like killing a troll with a stick; the plane tries to regenerate them and it takes a loooong time before it gives up.
Lots of psions expect to be able to reach godhood no trouble except that the planes need at least a square mile just to provide basic immortality; that takes around a millenia with the Genesis power. Now you just need to find a way to stay on the plane without leaving or going crazy. Some try to use "Magic Jar" type effects, which do work but most who go that route find themselves the victim of a claim-jumper.
Worshippers increase a diety's power when they die by increasing their plane's "mass." Prayer, rituals, and sacrifices have a similar affect.
Spirits are divine beings that are the living embodiement of a concept (war, death, truth, lies, deception, good, evil, law chaos, etc) on a material plane. They are immortal in the "don't die except from murder" sense but if slain the Spirit of X is not restored. Instead the next living being native to that material plane who is the epitomy of X becomes the spirit. Sometimes it takes centuries for a spiritual post to be filled but often the high priest of a spirit iherits the role. No guarantees though and
There are differences in the clergy. Deists must be within 1 step of their deity's alignment. Deities are also more likely to help out a follower since they want their souls (mwa-ha-ha.) Spiritualists can be of any alignment compatible with the ideal (there are no neutral followers of good, for instance but there are priests of Combat for all alignments) but the spirits have no compunction to support the clergy or even acknowledge them! The priests follow the Ideal, not the spirit.
Deist priests go through training and swear mystical oaths to their patron. Spiritualists go through a ritual to contact their Ideal. You choose a god, you find your ideal.