First, the character who wishes to achieve divine ascension must be of significantly higher level than the average level of adventurer types in a campaign world.
Meaning that if your character exists in the Forgotten Realms, he has to achieve roughly 120th level.



But seriously...when you get into the higher level campaigns where divine ascension even becomes plausible, the average levels are in the upper teens. As it says in the book, if 15th level is the average in the campaign, then the character must hit 25th - 30th level.
Now this certainly rarely if ever happens. How many people have legitimately gotten a character to 25th or 30th level?

Secondly, the character's ability scores should be on a par with demigod-like scores. Which means lots of 20's, 21's, etc. Again, how many characters manage to get most of their scores into the 20's? That's damn near impossible in a sane campaign!
Third, the character needs a body of sincere worshippers. How does the average character manage to get such followers? It would seem that most characters will never be in any position to be truly worshipped. The book defines sincere worshippers as those who are "convinced of his or her divinity due to their witnessing of and/or belief in the mighty deeds and miracles which he or she has performed...".
How many characters manage to have normal people witnessing the "miracles" the character pulls off (killing the lich, defeating the dragon or demon, etc)? Again, this isn't very likely.
Fourth, that character must have been true and faithful to his alignment and his god. Not many characters manage to avoid straying from alignment now and then.
Finally, after all that is done, and the character has fulfilled many quests, his diety will fill him with divine energy and ascend him to servant status. Note that at this point the character is not even a demigod! It says in the book:
"After several centuries of superior service and gradual advancement, exceptional servants may be awarded with the status of demigod, which includes having an earthly priesthood and the ability to grant spells (of up to 5th level) to the demigod's clerics."
Emphasis mine. Several centuries! So when a character in a campaign ascends to divine status, in essence he doesn't become anything that affects the campaign world for centuries, meaning the player and the other players/characters never see him again. It goes on to explain that the gods use these new divine servants for more important jobs than answering calls for help from the Prime Material Plane.
So when a character in a campaign attains divine ascension, that character basically can no longer be used unless the DM starts a new campaign set hundreds of years in the future!
I've never liked divine ascension and the idea of mortals becoming gods, and these rules just make me chuckle when I hear a player saying he wants his character to become a god.
"Ok, no problem. Let me just tell you what you need to attain that..."
