This will be my first guide!

I use Vi as my main jungler now! She is very strong at ganking, and extremely fast without taking too much damage in the jungle.

Pro's
Speedy jungler.
Amazing ganks!
Can gank a lane that enemies are pushed on.

Con's
Reliant on landing your Q.
Takes getting used to when clearing camps out.
Tend to get focused late game.

Start with Denting Blows: The added damage of the is more than you would be able to get with either of the other two abilities.

Next is Excessive Force: Allows you to damage to everything within a short distance behind the first creep/champion hit. (You can get Vault Breaker instead if you want to lvl 2 gank.)

Vault Breaker: It's a very good ability for getting your jungle creeps in a line to use Excessive Force and clear em fast!

Smite is a must!

You can exchange Exhaust for Ghost, Flash, or Teleport, but I've had the most success with Exhaust.

Make sure you warn the lane you gank, so they can distract the enemies in that lane, and you can land your Q and get your kill, or force them to use their flash!

When you get your ultimate use it! It's very strong for ganking. Use this before you use your Q, because you land behind them, and your Q knocks them back more.

Sorry if this was a bit blocky, it was my first guide and I didn't exactly know what to put in. But this is what I follow for jungling as Vi!

Have fun, and happy ganking!