Ninjask's defense is close to zero, and can't endure any hit at all. It dies on the slightest touch. So really don't have it stand there to attack (unless it's OHKO), or double team as you have no defense to do so.
Ninjask- [def + / sp.atk -] @ leftovers/liechi berry
EV: Def and Spd
-swords dance
-protect/silver wind
-substitute
-baton pass
*note: if a berry is used, make sure that your hp is equal to a number divisible by 4, + 1
Lead off with substitute, then use protect, and repeat cycle to get off some free agility. Leftovers will heal you by quite a bit. If substitute is not broken, use swords dance. If you're not using leftovers, then just keep subbing until berry is activated and baton pass it to someone. Try to pull of the chain FAST, and baton pass asap if you are even lucky enough to get out one swords dance. Pass it to a sweeper asap before Skarmory/Suicune comes out, and hopefully the sweeper will have enough power to take out the pseudohazers before they pseudohaze.
Run at the sight of quick attack/extremespeed users, or rock blaster (Rhydon/Armaldo). Ninjask is doomed against these attacks.