@Starry-- I would say that you pin up the top layers and comb it carefully curl by curl, then do the middle layers, then the top.
Or get it all wet with hot water, brush it out, and re-set the curls... if you like torture.
I want to use my own hair for Rikku, but I don't think it'll be enough, should I get extensions for the braids and ponytail, or should I just get a wig for the whole?