Okay, this is the info that i've gathered from doing garrisons many times, mostly successful too^^ but notice the mostly ;P
Ok, general party setup before garrison:
m m m m m m
m m m m m v
--o--o--w x x x x x x x x x x w--o--o--
| x x x x x x x x x x |
-o--o o--o--
w w w w
---------------------
Ok, little astry art to help with the visulization here... the -- and o represent the outer walls of the outpost, the --------- is the inner building that the npc war wizards, temple knights, etc, stand by.
x = npcs that you need to protect
m = us melees^^
w = mages ;)
v = me^^
Now then, we normally go in with about 18 people, and there are normally about 18-20 npcs, i want to say 20-22 though, because i think they stand in two rows of either 10-11 each, it's been awhile since i last did a garrison though, and not being a mage job, i've never been too concerned with how many npcs there were, i was more concerned with keeping the mobs off them.
ok, that is roughly how we get into position before each fight, though sometimes our mages and melees are more mixed in, but typically the melees flank the opening, one, maybe two mages per group, the rest of the mages stay behind the npcs and over see the battle. We have one person kite a mob around until all the others are dead, all npcs are healed, and all hp/mp is at full, then bring in the mob and kill it.
Most of the melees have warrior subbed, i myself go in as a war/drg, sounds odd yes, but at lvl 20 i get an attack bonus and jump with a dragoon sub, add that in with all my att+ and str+ gear, and i am one of the most powerful DD in our group typically.
DD/tanks engage the mobs, and try to hold hate on themselves. Since everyone tends to scatter once the fight begins, i wait and see what mob the npcs are fighting, then i go after that one, kill it, the go after the next mob the npcs decide to fight. Because I'm the semi tank for the npcs, one of our mages always tags along with me to keep an eye on my hp, npc hp, and to help however she can.
KEEP THE NPCS ALIVE!!! You'll get more gil at the end of the fight, and better drops at the end of the fight as well. Someone on the main forum was saying they get 0-1 dragon chronicles and 1-2 pieces of garrison armor. Well we get 2 dragon chronicles, and 5-6 pieces of garrison armor. We typically lose only 0-3 npcs at the most, normally we have all of the npcs or else only lose one of them. Mannequin parts are dropped by the mobs and seem to be random, but very plentiful during the second wave, almost everyone tends to come away with 1-2 mannequin parts.
We do about 4-5 runs back to back as well, so everyone also comes away with at least one bit of garrison armor. Our lotting rules are simple, whoever dies gets first pick at the dragon chronicles, if no one dies, then it's a free for all on them, with maybe the person who started the garrison getting one of them, this tends to vary. mannequin parts are free for all since you can only hold one of them. If someone wants them for a mannequin and not to sell they get priority. As for the garrison items, if someone wants a piece of armor to wear, they get it, otherwise everyone lots on something until they get 1 item, then they wait until everyone has 1 item, then it's round 2 and they get to lot again, wait till everyone gets 2 items, etc. Typically works out very well.
stuff to watch out for:
never do garrisons outside your LS, the few times i've done so there was rampant chaos, people ignored the fair lot rules in place and walked away with as many as 8 garrison items, (only 5 people out of 18 got ANY items in 4 garrison runs, i still don't know why the leader didn't kick them when they still lotted on items)
lastly people get mad and will try to kill you all, by "accident" of course. This one ninja who was supposed to be our kiter was complaining saying that she wanted a bigger share of the loot because she had a higher chance of dying, leader said no and the ninja kept "accidently" bringing the mob that was kited close enough to the outpost so that the npcs would attack it, next wave comes before we're ready, chaos ensues.
so there's vyuru's general advice and garrison knowhow in a nutshell, hope that it can be of use to you taodyn.