Archer skills

[cgbspender]

Use Mage's Ballad as soon as the healer's MP is too low indeed. Especially when one of the healers died and was raised. Even if you have only 500 mp yourself, it will still help him greatly. (you don't wanna die due to a lack of cure because the healer can't afford it, do you?).

Also use Peaon, to regen TP for any melee who died, or when the fight is starting to last. It will help. You don't need to let the song flow eternally though, after 40sec or so, their TP's should be back to a normal rate, if not at their 100%.

And the third, Foe Requiem, is a powerful weapon as soon as you have mages in your team. It can be BLM, SMN, AND even healers when they're in dps'ing mode. Your song will increase their damage a lot, and the mages have skills among the best aoe-wise. You shouldn't deprive them of that opportunity ^^^ (Magic Def - 10%)
Be careful though, with Requiem Foe, not only it is a strong ability, but it aggro's enemies really fast. I usually wait until the tanks settled aggro well (after a few seconds, to give them time for their initial cycle)

You have a support class. Even your LB is designed for it (you have the same LB's as healers, ie Cure/raise everyone).
Also, as a bard, you can have Mantra, as a cross skill, improving every cure (+5%) within a range for anyone inside. Doesn't sound "too great", but it helps, in particular when a boss is casting a powerful Aoe. (works under Healing-Over-Time casts, such as Medica2 / Regen, now it starts to be more interesting, right?)
Second Wind is a nice cross-skill, it will regen your HP quite a lot. (At ilvl 120, Second Wind crit at around 1400 HP). Not much in comparison with a healer's cure, but will save your life countless times. (and will save your healer some mana for free!)

As a side-note, during actions, your mates may or may not notice you are giving them the buffs. To make it clear, as you don't wan't to see your WHM or SCH run at the very opposite of you during your manasong (would be far out of range), you should mention it.

I use the following macro to tell the party :

Mantra :

/micon Mantra
/ac "Mantra"
/p I'm using Mantra : All cures improve+5%

Mage's Ballad :

/micon Mage's Ballad
/ac "Mage's Ballad"
/p Using "Mage's Ballad". Stay in range to regen MP.

The /p line means "tell in party log", in case you're not familiar with macros. Your mates will receive the sentence you choose. The name of the skill between "----" can be auto-translated, that would make it best, so that anyone even with a different language will understand it.