Abilities:

Blast Shield: Vi charges a shield over time. The shield can be activated by hitting an enemy with an ability.
Vault Breaker: Vi charges her gauntlets and unleashes a vault shattering punch, carrying her forward. Enemy champions that Vi collides with stop her movement and are knocked back.
Denting Blows: Vi's punches break her opponent's armor, dealing bonus damage and granting her attack speed.
Excessive Force: Vi's next attack blasts through her target, dealing damage to enemies behind it.
Assault and Battery: Vi runs down an enemy, knocking aside anyone in the way. When she reaches her target she knocks it into the air, jumps after it, and slams it back into the ground
Vi's main build should be tanky0ness and damage.

EARLY GAME
Your E should be used only when a champion comes into range of using your E on a minion and it hitting them, when it is double charged it should deal some considerable damage.
Your Q can be used to fend enemy champions off or use it to close a gap to get some direct hits with your W. However after landing your 3rd W hit early game, you should go back as the enemy have probaby began retreating.

MID GAME
When you get some points onto each skill and frozen mallet, You can easily pull of some ganks onto mid or tank a blue buff, It allowes you to spam your E quite a bit more. However if you decide to take it more to the jungle, Using your Q, E , E , R combo can enough damage to land the laner a kill.

LATE GAME
If by now you havent gone positive then un-install the game. When You Have at least black cleaver you are looking to initiate team fights or picking off some of the tanky-er champions to do some fast damage to. Your should also use your ultimate and ghost to catch some enemies running through the jungle

extra tips~
Stay in the bush quite alot and wait, especially on mid. You can land of a Fast kill with a team mate by succesfully ultimating and then Q, E, E .

~This is my first build, be gentle:D