#1, buy Call of the Wild.
Then, max out the lines of Spell Casting Mastery and Virulent Paralysis. Buy Natural Durability 3.
Once those are done, what you're looking at is the long grind section of Shaman AA. Pretty much a steady growth of power as you accumulate healing & defensive & offensive aa. I personally feel a pressing compulsion to finish lines of aa once I start on them, so when I did healing, I did every healing aa available before moving on; from a power per point spent perspective, though, you get the most from buying things in expansion order. All the Luclin stuff, then all the PoP stuff, etc. It's entirely up to you which order you pick, the long road goes many ways, but it all ends up in the same place.