Along with the ideas above, I think there's the self directed path. Although a simple recipe, I think this road would take considerable time (however I guess there's the possibility of very sudden achievement).
It reqires two crucial things: the accumulation of power considerably beyond peers or fellow mortals, and aquiring imortatlity. The accumulation of power in and of itself may lead one to the secret of immortality. Once immortality is achieved one must continue to accumulate power. The threshold of accumulated power for one to be considered a God is probably variable (and depends upon ones personal definition of a God).
The accumulation of power can be through knowledge, physical objects of power, and through influence (to name a few).
Immortality may be achieved through advanced knowledge (ascension), the use of an object of power (magic item, artifact, etc.), powerful magic (whether self cast or cast upon), or through technological advancement.
I think this would be very rare due to the long road one must travel, and the pitfalls that could end the quest forever before success is achieved. Pitfalls could include; dying while attempting to aquire knowledge or power; destruction by another power attempting to stop one before achieving godhood; inability to find the required knowledge or power.
To me, this describes the route many powerful wizards pursue, espcecially those that choose lichdom.
A non-spellcasting type would probably have to go the course of finding an item or some type of magic (potion, spring, etc.), or discovering the existential knowledge or realization required for ascension (spiritual, philosophical, nirvana, etc.) in order to achieve immortality - and then use the time granted by immortality to aquire the power necessary for godhood.
Of course, this is all just hypothetical and in no way related to my personal experience.
(...or not)
