Character

I find that cross class skills make battles slightly easier. In the case of Warrior I can't imagine not having provoke. It seems mandatory endgame.

Here's a list of the ones I like:

Paladin
-Stoneskin (CNJ lvl 34)
-Foresight (MRD lvl 2)
-Mercy Stroke (MRD lvl 26)

Warrior
-Provoke (GLD lvl 22)
-Convalesence (GLD lvl 10)
-Mantra (PGL lvl 42)Stacks with mantra for a bit of extra healing
-Featherfoot (PGL lvl 4)
-Awareness (GLD lvl 34) Don't want to get critically hit during Caduceus stacks!

Monk
-Invigorate (LNC lvl 22)
-Blood for Blood (LNC lvl 34)
-Mercy Stroke (MRD lvl 26)
-Fracture (MRD lvl 6) DOTs! DOTs! DOTs!

Dragoon
-Internal Release (PGL lvl 12)
-Mercy Stroke (MRD lvl 26)

The image above is from Reddit. The maximum you need to lvl a subclass for all their cross-class skills.