Tips to get an S as a jungler?

So I hit mastery 5 on ...kinda it. the other jungler I play is and I am mastery 5 on him too. but for SOME REASON (rito plz.) getting an S when you rank up gives no token. though I want a high mastery on skarner mainly for the mastery BM if somebody starts off by saying "skarner ew" in all chat [slayer-pantheon-thumbs]