Well, after someone told you what to take, and not what to do, you said that it certainly helps.
After I gave you advice on what to do, you completely ignored it.
Here it is again.
Speaking of the simple tactics of the railhead, deploy behind cover, always move more than 6", point, and shoot, the same can't be said for the rest of the tau units.
Here's something it took myself and others a while to learn. The first priority of stealths is to keep them alive, the second priority is to shoot them at something. Naturally, with 3 shots each, it wasn't easy to realise this. But if you can just trust me, it's the best way to play them. Never deep strike them.
Against guard, if you can find a piece of terrain to walk into (difficult terrain test), shoot, and jump out of, they're devastating.
Crisis suits have different tactics depending on their configurations. Deathrains are the easiest to employ jump shoot jump with. Fireknives take a little more thinking about the terrain, considering they need to be 12" closer. Twinlinked plasma rifle suits are best at 24" until you can be sure the unit will be very weak after being rapid fired. I would usually recommend against deep striking crisis suits.
Crisis suits shoot at sentinels and chimera's and storm troopers, they're not that usefulagainst guard. Keep them behind cover.
Fire Warriors are quite useful against guard, you can easily target a flank with a couple of units in fish and wipe it out. Shooting devilfish become really handy as well, killing 2.6 guardsmen on average each.
Kroot are great at cutting up guard in combat. They're great at shooting marines from cover, great at combat against guard. Remember the difference. Assault guard.
Gun drones are fun against guard.
Pathfinders are very useful at markerlighting units in cover. Against guard, a markerlighted submunitions can devastate guard bunched up in cover. It is best that the pathfinders hide from nearly everything though, they are often better behind cover where they can only see a fraction of the board than in cover.