Learnings of the Shas

Space Marines part 1: Tactical Marine based infantry
Space Marines have some of the hardest infantry in the game at the moment. Toughness 4 and a 3+ save will protect them against most things the Tau army has available. Plasma Rifles on suits are an option but at a pretty expensive points cost and only Bs 3, you're not going to kill a lot if you base your army around this weapon, though it does have it's uses.
 De-meching and trapping
It is vital to use the vast amounts of high strength fire power in a Tau army when taking on the Emperor's Finest. The crucial point with Infantry is making sure they're on foot. Blast apart transports and force those
Marines into the open. This gives you two advantages. The first one, pretty obvious, is you can now directly target them. The second is you've slowed them down. Marines won't sit around vs Tau. They'll try and get up in your face and assault, where your fancy shooty trickery can't save you.  If the Marines are caught out in the open, they have to dance to your tune. If they choose to sit still and fire at you, move away. Use your superior mobility to make sure they are out of range. If they want to move, they're not shooting. Draw them into positions where they are unsupported. Isolate them and systematically destroy units by focusing your firepower on one squad and blasting it into oblivion.
Screening
But not all of the Marines will die before they hit your lines. This is where kroot and sometimes gun drones come in. These guys are your expendable screen. Charge them in to hold up that assault squad and buy you time to make your escape for another round of shooting. It is important to note that you should avoid being charged yourself. The last thing you want to do is let the opposing player leap frog towards your lines, using the extra 6" to close you down. It is sometimes advisable to infiltrate your kroot screen to gain that precious few extra inches for you suits to deploy in but play it carefully and think before you deploy.

Part 2 will be up tomorrow where I'll be talking about tanks and terminators.
Ko'vash