The most useful tactic thus far has comprised of the mis-understanding of the goals of brenner.

The three goals to winning any confrontation are: Gain the "Tempo", Hold the better "Position", Make acceptable "Sacrifices".

Gaining the "Tempo":
What the party should get in the habit of doing...

During the 45 sec cooldown before the match, buff up. This will save you time, and might make the victory decicive. Already your at an advantage over players who haven't buffed up during this time. When brenner starts you aren't "Preparing for Battle." so by having pre buffed before being warped to your team's side, you can run head long into a tactical advantage without slowing down. The other team is now required to buff before engaging you which is wasted time. You know have had x number of seconds longer to move into a better position.

Holding the better "Position":
"Position" is the understanding of all things Time, Space and Value.

Time: the use of time appropratly can gain you huge tactical advantages, especialy when playing something such as regulation chess or Brenner which are both timed events. If your opponate is forced to setup hastey counter attacks to avoid losing, they will be miss managed and there flanks can be easily turned.

Space: this is the understanding of distance. How far is it to the intended target from the spawn? How far away is the enemy camp? Where is the first target. If the mechanics of the team aren't working towards the same goal, you'll see your position soon routed, and on the side of a loss. Organize your goals... try and be of one mind. Arguments too result in loses.

Value: Know what everything is worth to you as a working piece for your team, know what you actual worth to the team is. If your a mage and you get items that cure blind toss them, they serve better function on the ground than cluttering your inventory. If your a whm know what your role is? Are you curing? are you a deversion? Understand what your death results in for a lose of resources for your team. Protect more valuable "Pieces."

Ok enough of the broad talk on tactics lets talk specifics.

Mages will want poison pots and echo screens at near all times.
Melee will want poison pots and eye drops.

If your team has BLM set them up as what i'll call "Artillery" an Artillery will be defined as someone who does dmg primarly to a Flammen-brenner.

These Artillery will be the heart of your team... the objective is for them to spam on the brenner till it opens, and some one can grab the flame.

"Shields" are primarly melee classes, there jobs is to engage all targets that approach the Artillery. Provoke is very helpful...

"Picks" are support jobs like rdm and brd, who's soul job is to shutdown other mages with silence and sleep.

"Obsticals" are jobs like WHM and MNK, there job is to set up faints and bluffs... basically annoy the hell out the other side. they can seemingly run about, just to distract other players from there goals.

"Sappers" are jobs like PUP, DRG, and BST... they have the ability to add to your armies size... these guys are the grunts, they go where there needed and stay till the job is done.

"Runners" either players with alot of HP or def, or flee.. they capture the flag... er i mean flame.

So an actual layout might go something like this:

Artillery advances on the Beach Brenner, the shield move into position around the brenner enaging the poston... mean while the obsticals, sappers charge towards the enemy base camp, this will make them set up defense around there. allowing the beach crew to capture the flame much easier.

there are many statigies available this is just an example... but be willing to adapt according to the match set up.