After something like 3 attacks, Scathach does an AoE around her that melee should run out of her range for; there's no cast.
When she pushes you back, make sure to stay away from her should she teleport to you- her next AoE indicator is fast and will give a stacking debuff as well as hurt pretty hard.
Thirty Souls is a raid wide AoE and can hurt.
Sometimes there is a slowing debuff that also comes with a DoT. This can spell doom to those with it and Thirty Souls is cast (I've seen this claim a lot of people, especially if DPS is slow, she starts casting this combination a lot). Only solution I've found is to power heal through it.
Shadespin is always safe on rear and one of the positionals. Once you figure out which flank is safe, it doesn't change until you recommence the fight.

(See where the circle breaks on the striking dummy? A lot of people apparently don't know this, but that's where it indicates where rear ends and flank begins. You don't need to stand directly to the back, left or right to get those positions.)