^ What others have said, learn on when to use your songs and the duration. Always check the mp bar of healers. If there is mellee classes for dps, certain fights you may want or need to play ballad for a certain duration, turn it off as you may need Paeon.
Foe benefits basically whm, sch, blm, smn and even Ninja, so usually if there is 1 or 2 caster dps more then say a group with Monk, drg then i would prioritize foe over Paeon.
Invigorate, blood for blood, internal release, second wind and mantra are my cross class abilities i use.
Also note that your songs have a hearing distance so if you are not in the range of the group it is of no benefit.