Lakshmi.Alfredo said:
Around 40 you can just solo a FoV page in altepa and spin the -ni wheel, you'll get skill up fast enough.
He has a very good point, you can alos take on an DC or EM mobs and only use your Ni spells, while keeping shadows up at all times. This is what i did for a bit until i got sick of it taking it forever lol.