Any tips in playing Jungler particularly Evelynn?

So I've been watching KingStix for a while now and I cant seem to manage to clear all my camps in under 3:35 seconds. I always have difficulty in killing the Krugs like after successfully killing the big Krug the medium ones just went back to the camp erasing all my progress. I'm also having a bit of difficulty in killing the Gromp and the Blue buff at the same time. Whenever I killed the Blue buff the Gromp just goes back, even if I successfully managed to do this I always finish it at 4:05. So any tips in making it more efficient? how long does it take for you to clear the camps? and How do I beat the enemy jungler?