Gaunt the hell out of banshees and harlequins. Send genestealers after the lighter stuff. And land the hive tyrant on someone.
Skimming mech eldar are a tough list for tyranids...honestly I have no idea how you guys deal with that.
Actually, hormagaunts would make any harlequins or banshees they take almost pointless as you've got a much wider range than they have.
Although if you're just talking warwalker shenanigans, I'd suggest sticking to cover and taking potshots from warriors with devourers or the like. A WW can be harmed by those last I recall.
Also, raveners with death spitters deep striking can become VERY VERY obnoxious. Because if they survive that turn of "HALLO" than the eldar player can say goodbye to whatever squad it, or it's team mates are looking at. Just be sure to give them rending claws. So they can easily rip through anything the army has.
You can get alot more use out of other things than lictors. I highly suggest NOT using them if you can avoid it. They look cool, but unfortunately, you can get two raveners with higher survivability for the same cost.
Do you have any carnifexes? Eldar are really quite obnoxiously good at taking out infantry, but unless they're packing fire prisms and fire dragons, they're anti-MC isn't that great. Also with dakkafexes you can easily rend apart great swathes in the army. Just make sure to keep a shield of spinegaunts around him to avoid being charged by flying harlequins.