I am TwillyFSniper. I am Bronze V. Only Bronze V because I made seriously bad mistakes in placement. I truly consider myself approximately a Gold IV or so in performance level. I have: 2 pentas (both as Vayne, one was a 1v5 that deserves YouTube status), a decent record (other than ranked...), and about 450 games of experience. I am Level 5 with Vayne, with approximately 63K champion experience, and she has been my main for a whole year now, which, I'll admit, is most of my whole LoL run.

Here is a link to my record, on LoLstarz: http://www.lolstarz.com/summoner?name=TwillyFSniper&lo=na&l=en

Vayne is a highly mobile, squishy DPS-based, late-game carry and assassin with extremely high sustained single-target damage.

Vayne is a good pick when the enemy team has one or both of two things:
1. An easily cancelled carry that falls off before late game, such as Kalista or Ezreal. Vayne scales fairly fast, and never falls off if she's played properly.
2. Tankiness. Vayne has shred.

Vayne is completely based around the combination of MECHANICS. You'll learn how difficult mastering these mechanics really is when you start playing. Or if you already have, you should know.

Pros to Vayne:
*Vayne is fairly mobile.
*Vayne's late game is insane.
*Vayne has amazing capabilities 1v1.
*Vayne is quite the hard hitter.

Cons to Vayne:
*Vayne has one of the lowest ranges of any ranged champion.
*Vayne is easy to shut down early.
*Vayne only has sustained damage abilities.
*Vayne requires A LOT of skill to master.

Vayne's mobility is due to her Night Hunter's mechanics and her Tumble, each allow her to inch closer to the target. Vayne's intense late game is completely because of Tumble. Kiting and hurting all day long! Vayne's single target damage is nearly impossible to deny, her Silver Bolts procs on single targets, creating HIGH TRUE DAMAGE that can STACK with Tumble's damage boosts.

But, Vayne has a 450 range which can create problems particularly for laning, which is already plagued by the fact she can't really deal damage effectively then because her abilities scale with levelling and she's fairly item dependent. You need your DPS to really carry. Vayne's Silver Bolts procs deactivate if you don't focus on ONE target, and Vayne has only abilities based on her basic attacks, so she has absolutely zero multi-target damage. Playing Vayne IS NOWHERE NEAR AS EASY AS IT APPEARS. Vayne is a champion that requires great positioning skills, ability to figure out how to amplify her damage, and thusly requires A LOT of time to master. I still haven't truly mastered the art myself.

Good
Flash- This gives Vayne instantaneous mobility, which she has, but not as much as sustained chasing mobility. Defensive purpose, primarily.
Heal- All I really need to say is Vayne is the squishiest champion in the game (according to Riot, and the developers are often a good source of this kind of information). But I'll say this to explain it better: The ratio of Heal's effect to Vayne's Health max is one of the highest in the game.

Not Ideal
Ghost- Vayne already has sustained mobility... When chasing. So I guess it's a good escape maneuver? But there's Condemn and Tumble...
Teleport- Vayne does have early game issues, but defensive uses of Tumble can make these problems be not so much of problems...
Barrier- The shielding on this is fairly low, but Vayne is AMAZINGLY squishy... But there's always escape...
Cleanse- She does get tied up in CC a great amount of times, but Zephyr does have Tenacity... Also, being careful can let you avoid such...

Never Use
Smite- Vayne's Silver Bolts have a damage cap against minions. Jungle viability gone.
Garrison- DOMINION SPECIFIC. Exactly.
Exhaust AND Ignite- VAYNE HAS A GREAT PASSIVE YOU KNOW... IT'S CALLED NIGHT HUNTER AND GIVES CHASE POWER... NO NEED FOR CLUTCHING SUMMONER SPELLS THEN, RIGHT? CORRECT!!!
Revive- Unreliable. Unnecessary. Unviable.
Clairvoyance AND Clarity- Unviable. PERIOD.

My focus is:
Q>W>R>E

Tumble (Q): A vital part of Vayne's kit, the ability is a short dash that amplifies damage on next hit in several seconds. It is useful for tower-diving, engaging, and proc-boosting. It scales well with levels, so it is the main focus of the build, and is maxxed out at level 9.

Silver Bolts (W): Silver Bolts is a true (armor-pen) damage proc that hits for small flat damage and a percent of the enemy's max HP. This is used for potential damage stacking with Tumble, and for shredding tanks in fights. However, it's not strong enough to tank-shred with on it's own always.

Condemn (E): Condemn is an ability that knocks back the target a certain distance, counts as a Silver Bolts tic, and if it stuns an enemy into a wall, it deals damage. As it costs 90 mana, it is mana-ineffective to level early on. It's really only useful as an engaging or escaping mechanism, but only when you need it. No need to build Mana when you need DPS, LS, and Armor Penetration on Vayne.

Final Hour (R, Ultimate): Final Hour gives a temporary damage and chasing boost, as well as the temporary ability to go invisible while using Tumble. This is useful if you need extra leverage in a fight that you don't think you can get with your extremely high single target damage on it's own. I level the ult at 6,13,16 because you really don't need it like you need to max Tumble and Silver Bolts, however, it's great to take first level at 6 for a power boost of sorts.

Vayne has a huge dependence on her items, so this discussion is extremely important. Her items give her the single-target damage she strives on.

Start- Doran's Blade is essential for early laning. You need tankiness, you need lifesteal, and you need AD. Health Potions are necessary to keep alive while you build up the earlier parts of the core.

Early- Avarice Blade may have no Attack Speed or Attack Damage boosts, but gold income is a great way to start for Vayne. She will need it for sure. I will build this into a Statikk Shiv at the VERY END of the core build to take advantage of the extra gold. Vampiric Scepter gives LS and AD for a decent end to laning phase. Boots for more mobility to keep up with more mobile ADCs particularly (even though Vayne is indeed one of them). Finish items in this order: Bork, Greaves, BT, Shiv.

Mid-Game Core- Statikk Shiv is a great item on Vayne. It allows her to get needed CS at a faster rate than without it's passive that allows her to deal damage that goes through adjacent targets on a counter-based cooldown. BT and Bork combo- 30% LS, 120 AD, 40% AS boost, shield, double proc... everythin Vayne needs other than more AS and movement. Berserker's Greaves with Furor is a standard staple for ADCs, it gives decent movement and attack speed, and movement speed boosts upon attack. For an economical 1475 gold.

Situational Items-
Infinity Edge- Gives a LOT of AD, and high damage crits. Great for sustained damage. Sounds right up Vayne's alley.
Sword of the Occult- Vayne is extremely capable of a late game DPS-based snowball, with the highest potential AD boost in the GAME. It gives up to 110 flat AD.
Youmuu's Ghostblade- Gives a low AD and Armor Pen. boost, but it's useful for mobile DPS if you need more mobility or DPS. Active-based, with a 45 second cooldown. Fairly short CD for an active ability on an item... Hmm...
Last Whisper- gives large amounts of percent-based armor penetration (35% of opponent's armor) to create less reliance on proccing, and a moderate 40 flat AD.
Trinity Force- I used to condemn the usage of this on Vayne. However useless AP is on Vayne, the Sheen can stack with Tumble's damage boost.
Zephyr- a nice all-around Attack Speed centered item. Gives the best percent-based movement speed boost in the game. Build if you sell Greaves.
Phantom Dancer- Really nice when built in combination with another crit-based item, particularly an Infinity Edge. Also good if you need a way through your own creep waves.
Mercurial Scimitar- Gives high AD and moderate Magic Resist. Quicksilver is also nice to have against a high CC team, like if there was an Ashe ADC, a Talon mid, a Gragas jungle, a Malphite top, and a Nunu support on a team.
Banshee's Veil- Great for blocking out abilities you don't need to hit you, such as high damage spells.
Guardian Angel- The passive revives you, and it also gives moderate Armor and Magic Resist.

Ezreal- 1/10. Vayne can easily dodge everything Ezreal has to throw at you. Also, he can't carry well early, so Ezreal is EZ for Vayne to DEMOLISH.

Urgot and Kalista- 2/10. Urgot's kit is a kit a Vayne, particularly with a high lifesteal kit, will negate nearly all damage. Plus, his ultimate is nearly USELESS against a high ELO Vayne.
Kalista's functionality is based on the support, and how TANKY they are. Look at her ultimate and you will see. This makes Vayne have especially effective shredding. But do not ignore her mid-game prowess. Try to endure to late game, then you will be handsomely rewarded with a huge carry.

Sivir- 3/10. Sivir carries later with AD, based on her Boomerang Blade, which Vayne can dodge. Plus, Vayne requires less to carry.

Lucian- 4/10. Lucian is definitely a burst champion. This matchup is probably more a toss-up in higher ELOs because of Lucian's ridiculous skillcap, but Vayne can counter Lucian with higher sustain, and more carry ability because of Lucian's inability to kill efficiently in the hands of an unskilled summoner. But, when Vayne is bursted down, Vayne is not exactly going to recover easily.

Caitlyn- 5/10. This matchup is an easier toss-up for Vayne, as Caitlyn has the advantage early. But Vayne has the ultimate late game carry. When either attempts to cancel out the others mid-game, they have a large likelyhood of success, but Vayne has a better chance because Caitlyn is focused on her strong early game, than Vayne is on her late game.

Draven- 6/10. Draven is a more difficult toss-up. Vayne will have the advantage if the Draven is ineffective at farming with him. But, normally, Draven has the advantage. Able to out-duel her early, and late if he takes advantage of her early game weakness.

Ashe- 7/10. Ashe is extremely effective against Vayne, if she doesn't fade after her exceptional early game. The CC in her kit will make mincemeat of Vayne, if used properly. Particularly since the 5.10 buff. Her new Q allows her to outdo any ADC in DPS from 1-9.

Twitch- 8/10. His Deadly Venom damage bonus to attacks is really painful for Vayne. You cannot simply Tumble out of his Contaminate's range. He will out-carry Vayne starting approximately level 3. If you pick Vayne against a Twitch, please play safely if possible. However, this can turn into a skill matchup if you're good with Vayne.

Tristana and Graves- 9/10. Tristana is a menace for Vayne to face. Tristana's Rocket Jump will make her extremely difficult to plainly CATCH. Also, Tristana is absolutely ridiculous about having super high range later in the game. Tristana's attack range on it's own may cancel out a Vayne later in the game.
Graves has a range effectiveness issue. Against a Vayne, that's not a problem, because Vayne has short range. Also, Graves has super high durability for an ADC, you have to proc to deal a significant amount of damage. He can, however, just sweep you with Buckshot.

Varus- 10/10. Varus will nearly always win, unless he's a feeder.However, normally, Vayne is screwed for MULTIPLE reasons. 1. Varus has a skillshot that cannot be dodged simply. Vayne can tumble out all she wants, the Varus will still hit. 2. Varus has a good early game. This screws Vayne over. 3. Varus also has a high attack range, cancelling out Vayne.

Early Game- Vayne has performance that scales with item buys. Vayne's early game, therefore, is no good, as mentioned in the Pros and Cons section. Use your Tumble a LOT, I mean as much as possible and of course while saving mana just in case. Tumble is a good tool for farming, poking, and escape at this point. Good enough really if you aren't caught.

Mid-Game- Start becoming more aggressive as you compile your core, particularly after you get Blade of the Ruined King. This item is the essential of successful a carry in the build. Don't engage fights unless you see clear kills, but follow-up on engages as much as possible to obtain a carry.

Late Game- Just kill, kill, kill. Get situationals as you need them. See the Item Discussion to make a judgement of what you'd want certain items for.

Basically how a good game will go in a nutshell is that you get unbelievably fed by the end of Core, or usually late mid-game. You can outduel ANY ENEMY CHAMPION, even if it's an ulted Nasus. Of course, this is when it's going good. When it sucks, you'll know.

This is a great question. For Vayne, preferably tanky supports or damage boosters with great CC capabilities.
My top 6:

6. Nami- Nami's ultimate can be a huge help in teamfights, as it knocks back opponents in it's path slightly, as well as slowing them. she has a nice partner AD boost as well.
5. Sona- Sona is great for her damage boost, her stun is also of grand use to just pounce and get potential free multikills. But, some carry with Sona and that's not good for hypercarries like Vayne that need the end-game carry to dominate the Rift.
4. Leona- Leona has a skillshot stun that can be particularly useful in suppressing an opponent, either for a kill or to keep them away from lane (target their ADC, Leona). Leona also has a slowing AoE ultimate useful for similar purposes.
3. Thresh- Thresh is a unique one. Thresh is outstandingly utilitarian, in other words, useful. He has the lanterns, which you can travel to and then teleport to Thresh's location as well as be granted with a shield. His grab and ultimate combo grabs the target, travels to their location, then traps them in. Use this to kill if you can. But this is more particularly for higher skill levels.
2. Alistar- Alistar's knockup is perhaps the most useful CC for Vayne, personally. Alistar is perhaps the tankiest support in the game so he can block out damage. Alistar also has a light heal, which is useful.
1. Braum- Oh yes the greatness of the Braum and Vayne combo. Braum has a skillshot slow that activates his passive, which tics enemies to a stunning proc. Use this proc to stack your Silver Bolts, because it should work perfectly. Then kill them. It's a near guarantee it will kill or at least make them run away because they can't fight without being an idiot.

These three essential gameplay tips will help you on your way to become an excellent Vayne:

1. Combo. Use Tumble's damage boosts when proccing Silver Bolts or Blade of the Ruined King, or BOTH. Even Tumble with Statikk Shiv's passive for a nice split pushing effect.

2. Take advantage, and initiative on a possible kill situation. You can Condemn champions into walls and fairly simply pick them off.

3. Use your teammates' CC to advance on the target. Doing this with Tumble will allow you to quickly pummel the target down with a Silver Bolts proc or two.