Ascension is rather important to the world I am designing, so I came up with the following system for doing it. Note that some of the things I put in here, I put in because of the way the backstory in my world works. Specifically, the tasks that have to be complete before achieving a new divine "status."
My system is also slightly different than the main book, but that's mainly because WotC has published some conflicting stuff on the details of being a god.
To become a god, you have to bathe in the First River (which is really hard to do, but I won't get into details). That makes you a demigod, gives you divine rank 1, and one outsider hit die. You also get +10 to all stats, and 12 ability raises of your choice. I have every divine rank give one outsider hit die, one ability boost, and +1 natural armor.
At this point any worshippers you have start to give you divine experience points. Divine experience points let you raise your divine rank in the same way experience points let your raise your level. I haven't done details on how worshipper days translate into experience, because I don't need that for a while.
Each time your divine "status" (demigod, lesser god, intermediate god, greater god) would go up, you have to complete a certain task to actually advance in rank. To become a lesser god, you have to meditate/spar/hide/whatever in a particular hard to find place on the Ethereal plane. Becoming an intermediate god requires getting five other gods to assist you in a ritual rebirth. Becoming a greater god requires getting another god (at least intermediate) to give you a divine rank.
Becoming a demigod give you 5 ability raises and +3 natural armor. Becoming a lesser god gives you 10 ability raises and +5 natural armor. Becoming a greater god gives you +5 natural armor and 15 ability raises.
Part of the reason I did it this way was to increase the disparity between gods of different rank. I also have no requirements besides certain actions because I like the idea of a really weak god (like the god of beggars WotC did up).