This is my first guide. As a Vayne main I have some experience in how to play her both in lane, teamfights and just in general.This guide is more of a build, and little about her mechanical tactics, as it's hard to help someone become well in tactics. Just use your head, and maximize utility and mobility and you will be fine. Time and dedication is what makes the best Vayne players. Play a lot of vayne, in every kind of game mode, and just get a general feeling of how the character should be played.

Cons:
1) She is really squishy early game.
2) Has a hard time laning against long ranged characters.
3) Vulnerable against champs with vision abilities when using her ultimate.
4) If she falls behind, she probably won't have an easy time getting back.

Pros:
1) Extremely hard carry if played right.
2) Has a good ability kit, a stun, a true damage passive, increased movement speed and mobility abilities with an invisibility and damage increase.
3) Good at last hitting.
4) Insane good push as her q can be used on turrets for extra damage and basic attack reset.
5) Extremely fun to play.
6) Strong late game duelist.

In teamfights it's crucial that you don't get caught out of position. If the whole enemy team is focusing you, tell the team to focus their carry, and tumble away with your ultimate up so you prock invisibility, then get a distance away from your team, and then engage when they switch their focus. You are a tank demolisher, so you shouldn't be afraid to fight em off if you are fed. What's important is that you always focus their carry, if you hit a stun on the enemy carry, you can take advantage of that and kill their carry, then switching the focus to another character.
Making your team peel for you is very very important. You are a strong teamfighter, but not strong to focus more than one character at a time. Most importantly play safe against a long ranged opponent, and don't feed, since it will be a lot harder to get back into it with Vayne than some other adc's.