I am a TAU-player myself and my number one advice is to take out his crisis suits as fast as you can, they are the ones that will punch holes in your line. However, this is often quite difficult because of their jump-shoot-jump movements. Try to force him out of cover and when you can lay some fire down on them they shouldn't be to hard to kill. Another good idea is to swamp them with scarabs. Turbo-boost them inte some cover and then charge. A big squad will probably kill the suits but even if they don't you will lock them up for several turns.
Another thing to look out for is big kroot squads. If he charges you with 20 kroot he will get 60 st 4 attacks, and that can hurt even your big warrior squads. However the kroot are easy to deal with if they are out in the open, since the go down real easy to normal gaussrifle fire.
Your destroyers are your biggest asset, they can kill tons of firewarriors and anything else he can throw at you, but try to keep them close to your main force since they are easy to kill if they get isolated.
Keep moving your warriors forward all the time without hugging to much cover. They will draw a lot of fire away from your more fragile and tacticaly important units.
Hope it helps
/Tokugawa