Technically speaking given how geared players are these days, ballad is not needed. For my team I just play during Phase 1 after the adds are killed to intentionally control my DPS so that Phase 2 starts exactly after Twinny use Death Sentence.

You might want to discuss among the DPS members of your team on how to deal with the snakes. My personal take is for BRD to take the big snake full time. Small snakes are really easy to down especially if you have a BLM or SMN around (SMN DoTs OP, while BLM can manawall and stay inside the pit to DPS) but most team wipe due to big snake not dying. BRD's advantage is 100% uptime so you can continue to DPS during dodging divebombs and when MT pulls it to the centre for LB etc.

You can choose to Foe Requiem during the snakes phase. However no hard and fast rule with regards to songs. Personally I trust that my fellow DPS are up to standard with their DPS and technically does not need Foe Requiem. Anyway my team is 3 physical DPS and to Foe for a single magic (SMN) is pretty pointless. If it's a BLM maybe yes if snakes was an issue. Reason being for progression purposes, your healers are more than likely to need your Ballad than anything else. I would encourage fellow bards to watch out for healers and use your MP for that. Save your battle voice for times when your WHM's MP drop too low or when a healer dies (especially to twisters) and you need to boost back their MP after resurrection.

Other than that, there isn't much tips we could give if you already knew your job and your DPS "rotations" (knowing what to do and what to use at what time, maintaining DoTs etc). As a BRD you don't have complex rotations to maintain like DRG/MNK, nor have to watch for MP BLM nor needs to heal etc. And if you're good you can play partially "blind" and need not stare at your hotbars. So if you're on voice chat like Teamspeak, help to call out for DS/Twisters/Dreadknights during Phase 4 and for Phase 5, calling out Hatch (some players don't even know they got the hatch icon) so that players who got it can prepare to enter neurolink in case OT isn't able to intercept it.