There is no order to most of the last half of the Main Quest. I've indexed it by trial, but that's just for my own convenience. The only "requirement" (see the Hiccup page for why it's not) is that you get yourself named "Nerevarine" by each of the four Ashlander tribes and get named "Hortator" by each of the three Great Houses. The order in which you do it (or if you do it at all) is entirely up to you.
You may have already spoken to the Ahemmusa Wise Woman on a quest for Skink-in-Tree's-Shade at the Sadrith Mora Mages Guild. If so, you know that there is no love lost between the Ahemmusa and any non-Ashlander, even if he/she is Nerevar reborn.
The Ahemmusa camp is on a little spit of land on the far northeastern side of the island. It should be marked on your world map. The Ahemmusa have no Ashkhan, so you would do well to follow custom and speak to one of the gulkhans (Kausi, Dutadalk, or Yenammu) before going to the Wise Woman. But I do not see anything that would prevent you from just going directly to the Wise Woman.
The Ahemmussa are in a bad way. They have no Ashkhan and are troubled by blight. The Wise Woman wants you to prepare a place of safety for the tribe in Ald Daedroth, a daedric shrine two or three islands north of the camp (you must come here on the Pilgrimage of the Four Corners in order to become Archcanon of the Temple). After making Ald Daedroth safe, she will name you Nerevarine. Just what, exactly, is "safe"? She doesn't say.
As always, there is a bit of a complication. The shrine isn't unoccupied. In fact, it's occupied by two different sets of folks: Ordinators and daedric cultists. At the moment, they are too busy killing each other to take much of an interest in you, but that won't last long.
As you enter each section of the shrine, the two groups will have at each other. You can side with one or the other or just stand back and watch the action. If the Ordinators win the engagement and you have some rank in the Temple, they will usually leave you alone. If the cultists win the engagement, they will attack you. My recommendation is to let them beat on each other and then mop up the survivors.
Be sure to talk to Ra'Gruzgob in the uppermost chamber at the shrine. He's an Orc that thinks he's a Khajiit. If you give him some Moon Sugar (like he really needs more of it), he'll point you to Gambolpuddy, a daedric artifact that increases half of your attributes while decreasing the other half.
Ambitious Morag Tong members will be interested to know that there are a couple of the Threads of the Webspinner in Ald Daedroth. Two daedric cultists (named "Doomba" and "Gnaw Tooth") have the Ring of Sanguine Green Wisdom (Gnaw Tooth) and the Belt of Sanguine Smiting (Doomba).
Officially, you can make the shrine "safe" by clearing out those sections necessary to get the Wise Woman safely to the statue of Sheogorath in the center of the shrine. Anything else is just gravy. But what a load of gravy - every Ordinator has some Indoril armor and a Demon Mace (enchanted Ebony Mace) and most of the cultists have something decent. There are a ton of offerings at the various statues and a few obligatory daedra with the obligatory ebony/daedric weapons.
After making the shrine safe, head back to the Ahemmusa camp and have the Wise Woman travel with you to Ald Daedroth. You'll need to protect her from Cliff Racers and whatnot on the way, but once you have her in the Inner Shrine, ask to be named Nerevarine and she will.