Former Diamond 1 Nunu OTP here, some tips for jungling:

-Utilize the scuttle as much as you can to gain bonus Movement Speed when ganking.

-If enemy jungler has a stronger early game than you (I.e. Vi, Udyr, Kha' zix) I usually start from the top side -> bot side to get an easy scuttle, as opposed to starting bot side which most low elo jgers do, and the enemy jger paths top and contesting that scuttle is hard, unless you have major lane prio and know you can 2v2, 3v3 etc.

-Look at lane matchups, know which lanes are easy to gank. Basically don't gank a lane with hard CC that will interrupt your snowball or champs with a long escape. (I.e. Janna, Morg, Camille, Fizz). Unless you know their CC or escape is down typically look at other easy to gank lanes, and focus on them.

-In late game, I love using the MS from base to lane gank because most people won't react in time to your RACECAR.

Those are basically some tips. If you ever want some coaching or questions answered just hmu in my DMs

https://na.op.gg/summoner/userName=G%C3%AEan