Hi there. My ign is faker pls no. I was a plat 1 jungle last season and my favorite jungler was vi. She bring so much to a team and also has a very strong carry potential.

Early game, you have so much gank potential. Even after the enemy flashes you still have kill potential with Vault Breaker plus redbuff. You wanna throw as many ganks as you can early, you can guarantee flash or kill if you land q nearly every single time.

Mid game you wanna target their hard carries. You can 100 percent zone a carry completely away from your team either killing them or guaranteeing your team taking no damage. Mid game there are really no carries that are just gonna blow you up unless they just are fed out of their minds.

Late game- Now here is where it gets tricky. As vi you can peel so well. But you have to decide what is going to work better for your team. You zoning their carries or you peeling for yours. An ezample of when to peel for your carry is if they are really dominating and you have faith they can clean up the enemy team. Example of when you wanna go after their carry. When your carry isnt that strong or your carry is already getting peeled for ie thresh leona. Or if you just hit like a brick sh*t house and you can just 100-0 their carry do it.

Vi syngerizes well with teams that have all in. Mids like orianna katarina or yasuo synergize extremely well with vi being able to follow her hard engage. You actually dont need much synergy with your top lane but good top lanes would be heroes like jayce ryze maokai and ali. People who can all in or lock people down help with vi's hard all in.

If you read into the notes (where i put most info) you can see i talk about some of the "best" items on vi. While this is holds true being that randuins is the best for armor, banshee is the best for mr and tri force is the best for damage, bar none. That doesn't mean you have to build it. Tri force is a very very strong item on vi. It fits her abilities better than perfect. But that doesnt mean you always build it. So here is when and when not to build certain items. If you start out the game and you're 1 snowballing, or 2 just not dying after your jungle item going tri force is ok. If they have an ad mid and top going tri force is definitely recommended because it is easier to build just armor with a tri force then armor and magic resistance.
WHEN NOT TO BUILD TRI FORCE.. -- So if you start out just dying a lot, tri force is way to expensive to still get, you clearly need to build tank over tri force because youre dying for a reason. Another reason not to build tri would be if your team was snowballing hard and you weren't getting a big source of income. Then you can go straight into tank. If you dont build tri its always smart to grab a hexdrinker (taking ap damage) or a sunfire(taking physical damage) These items give you some durability while also giving you the damage you're gonna need to successfully zone those pesky carries.

Early game you wanna throw out as many ganks as you can because of how strong your gank potential is, but you can't forget to farm. So many people just stop farming and lose out on so much gold. After you gank enough early you can farm your jungle as much as possible throwing out ganks only when someone is overextended or you're just sure you can get a kill.

Pros

amazing gank potential
strong early game
great stick
zoning potential on any carry
one of the strongest initiators
Gives many handies
many build paths

Cons

Only has all in
Item reliant to be effective at zoning
very very reliant on q landing