They're big and slow.
Let them run into your saber, sniper or just blast away at their heads. You could whittle them down with cautious gameplay, which I really dislike.
I kill my wookiees like I kill my dekas, out in the open with no cover and a gun. That's actually pretty fun. Strangely enough, dekas are easier to out-shoot most of the time.
Only other tactic is when they switch to melee you can:
a) turn around and run, throwing potshots around every time you get enough distance or turn.
b) hold you're ground and fire at their big, fat, hairy heads. You almost have no choice but to do this as an sbd. They used to be able to knockdown wooks I believe but now...
And sbds can mitigate melee dmg from wooks by purchasing the heavy armor. Works against sniper shots, nades, rockets and wooks melee.
Chip away at them or outmuscle them if you're not gonna saber or snipe.
Only other bit is that they take increased dmg from being set aflame. Especially if they're Raged.