Some good advice here and some optional advice offered as "mandatory". Must be an internet forum!
Absolutism aside, I think the question was HOW to play them.
What I like about Tau is you can effectively give the enemy bait and when they take it, be behind them. Time is the best friend of Tau. Once the enemy is committed to a position and broken apart, you can attack the weakest links and bring overwhelming force there and then across the enemy line.
In my case, I deploy half the force. The other half stays off. The half on the board is tougher to kill and damage dealing enough that the enemy cant ignore it. I've seen Broadsides with Heavy Rail Rifles, and Riptides, both do well in the role of bait. I think tanks make a much poorer bait since they can be one shot'd. One can argue the difficulty of this all day long but the reality is they canbe, and Broadside units with Drones (or a couple Riptides) cannot. Tactically a better gamble than tanks.
If the enemy has, let's say, 12 units it's a near certainty that they will have 2 Scoring units at or near their own backfield to maintain the objective there. Probably at least 2 to the fore. Assault and other units will be dispatched to silence the isolated Broadsides conclusively, for unless they beleive in winning the lottery, it seems silly to try and outshoot the Tau. So then you end up with at least 4 pools of units, more or less. Each pool can at most bring 3 units to bear on its "sector" by the time turn 3 arrives. The clock is now ticking.
The avalanche of force is then brought from reserve against the weakest and least defensible enemy pool of units to ensure they will have feeble at best response. In turn 4, they are wiped and in turn 5, a second sector will be with no one in range to EFFECTIVELY help it. At games end, you have used your position to win instead of just trying to outmuscle the enemy the whole game.
You CAN try to outmuscle them and you might even win that way. But learning how not to HAVE to will make mismatches a lot less relevent to you.
Obviously to pull this off, you need mobility and you have to be really comfortable with half or more of your firepower not present for a lot of the game. It takes a bit of faith and experience to really find the comfort with that. Thats why so many people just don't do this. But more are catching on.
But as for how I fight with Tau: That's how. My regular opponents know its coming. My regular opponents recognize that I will lose half the firepower I own for a goodly part of the game. They desperately want to take advantage of that fact. Unlike Gunline Tau, they dont have to worry that I will hide behind a fence nor blow them off the board. So they will sometimes try to control the middle and counter what I'm about to do by "sticking together" and waiting for the monsters to come from the corners, so to speak. This has disallowed them from silencing the Riptides or Broadsides pretty often, due to range issues and they run the risk of being pretty exposedto what IS on the board while they wait. In the case of Broadsides, the enemy is picking up vehicle models round after round, but not "falling" for the bait. By the time i get there, they only have their normal units, which are prime targets for the reserves but at least they HAVE them to lose and then respond in more force than they normally could if they took the bait. Lists that rely too much on armor end up doing poorly when they do this though. Mechdar for example tend to do pretty poorly when they try this. So much of what makes those lists good relies on the hulls staying intact and thats tough to do with no cover save. Warp Spiders provide a darn good answer to this trouble because it can gety to the target unabated and through speed acheive kills and NOT be isolated. Warp Spiders are a hard counter to this concept, but here again, any kind of bad luck for the Warp Spiders is pretty disastrous. they have to kill their target on the drop OR ELSE and of course if its a Riptide we're talking about, the Early Warning Override could make for a much lower than average performance by the Spiders. Still, it's a good counter.
Don't know if that helps, but there ya go.
Also:
Tau Flyersl
Tau listiness