The Guide To Fighting 'Nids:
Don't take board sweepers, 'Nids take apart heroes and big units like so much putty, you can spend 400 points on the command squad from hell, but for 200 points we will take the unit who will sacrifice itself to shred it. And then we have 200 points to go to town on the rest of your army.
Bolters baby, bolters. Nothing scares a 'Nid player like a line of bolters who know what to do. Sure, we might disrupt your lines and break them, but as long as you are putting bolts down range you will come out the stronger. Stand and Fight, never run, and for the love of god keep shooting.
Vehicles, We can only glance a vehicle from range, really, unless we get claws-to-steal we can only glance, under new rules we cant destroy them with guns. So, piling your tactical squads or fire teams into cars and driving away lets you begin the meat grinder anew and bring the beast down.
Shoot the big ones, Bring down the synapse, disrupt the gaunts, how much simpler can it be?
Dont bunch, bunches are lunches. Nothing makes me smile more than a brood lord eating his way through squad after squad who have no room to shoot him. If a unit is engaged in close combat, get the frak away, and shoot them down when you guys are dead. NEVER TRY TO AID A SQUAD IN CC WITH 'NIDS! More will just pile in behind you and soon enough you have no units whatsoever, and nids are wiping gristle off their claws.
A good tyranid player will make you dance to his tune, the key is to not let him gain advantage by scoring easy kills. 'Nids win by tilting numbers in their favor with skill then just eating their way through everything. Do not let this happen, save men not rounds, shoot them all and stay alive, once enough are dead we, the hive mind, are defeated.
there we go, don't tell your freinds.