Well, I am not going through FOC in the order I thought, actually I am just going on down the line on my army list that I printed out, which I guess means, troops before suits, but then my Kroot are at the bottom of the list, so oh well.
Firewarriors! And Devilfish. Some people say the fish is over-costed others say firewarriors can't do anything. I say that , yea maybe the devilfish is a tad expensive, but then I look at the sillyness of the price of the disruption pod, I think that it is a good points cost for a tank that can act as mobile cover for the rest of my army, AND get a +4 cover save itself.
I usually field Fish in a scorefish config (no bells or whistles other than Disruption pod) However I take 10 fw instead of the usual 6 for a scorefish.
I play mech Tau all the way (one unit of kroot, outflanking is nice but I will get to that later) Generally I keep all of my FW in fish, some games they never see the light of day. Fire warriors have good range and you can set them up in a pretty formidable gunline with broadside and markerlight support, but with all the drop pods, mycetic spores, and super fast troops (hormagaunts!?!) a static position will be overrun in no time. In general I shouldn't let my FW out of the fish unless they are going to FoF leftovers. In reality I push these guys to their limits a lot, and sometimes it pays off, and sometimes it goes poorly.
For an aggressive general there are a couple things of note. A scorefish is a dual sided sword, and kind of a funny name, because in an annihilation mission, score fish are just that, a bunch of points for the enemy. They give up 1 more KP versus a standard transport of a different race because of drones. This is a bummer, and in most kill point missions my strat is KP denial so I reserve these guys and try to keep them off of the field using positional relay. I could field them with smart missile systems, but to make that worth it I would also slap on a targeting array and multi-tracker and that gets too expensive for me. Plus with defensive weapons classed at S4, I could only fire one weapon and I really want to keep moving.
So back to the KP thing, keep these guys reserved. In the other two mission types, drones are a ton of fun and if used right really help control the enemy's movement. General drone tactics include: getting your opponent to shoot at them, getting your opponent to assault them, sitting them on an abandonded objective, blocking a retaliation assault on a double FoF (i have done this more times than I should have but who can resist 40 S5 shots at a group of oblits!? gotta love those cover saves getting in...)
Since drones count as disembarking from an open-topped vehicle you could assault with them after a move, but a squad of 2 drones will die to anything so it is better to have the enemy waste their turn assaulting or shooting these guys. (Different story with piranha squadrons...)
The devilfish itself is a pretty big tank. Armor front of 12 will keep it alive but it's width is where the money is at, those big hips are perfect for hiding a squad of suits. Old Shatter Hands does this better than me with his "circling the wagon" which I am completely stealing now and having more success than what I was doing before.
In summary I use the drones to be as annoying as possible, the devilfish for mobile cover and to keep my firewarriors safe, and suits with cover.
Firewarriors, the way I use them, are super Mont'ka. Its all about the killing blow, but knowing where to strike is a key element. I still FoF, but it is less powerul, but using Mathhammer i can tell you this- you will kill 1.5 MeQ on average with a FoF that has 10 FW, in other words, don't FoF anything other than leftovers, and unless you have some drone coverage don't FoF assaulters. Pathfinders make this better, but it is still risky.
I like fire warriors, but I just can't seem to take advantage of that 30" range. I am all about the "no guts no glory" FoF, and I can't bring myself to have my army sit still long enough to fire 30" away.