For better or worse, I play Tau, so here's what I'd say.
Get into close combat and the game is yours. Seriously. Suits can sort of hold their own against basic troops, but everything else in the army will roll right up in CC.
Watch out for flechette dischargers on the vehicles. They cause auto hits against charging enemies, and I'd always take them against 'nids.
Railguns will really mess you up, but probably mainly from tanks, which have the submunition option. Broadsides are hella accurate, but against anything T6 or up, they won't auto-pop it, and they don't do multiple wounds, so monsters shouldn't be too afraid of them.
The bread and butter of really any Tau army are the Crisis suits, which will jump around and lay down some serious fire. Corner them and lock them in CC as fast as you can.