Spy in competitive and playing a simple Valve Pub has a completely different mindset. In competitive, you'll be using your revolver extensively: every single point of damage matters.

Most important target: the medic. Medics have ubers, and ubers can push you all the way back to spawn. Getting damage on the medic for a soldier to take him out, or even you, is always a great thing.

Now besides the medic being obviously your most important target, there are several other calsses that can be just as important to pick at key times. The closer to the other team pushing or the closer you are to pushing the more important getting the pick gets. I use the following pick order

1. Medic (more when closer to full uber)
2. Demoman, Heavy, Engineer. (demo on attack/defense, Heavy more on defense a bit less on attack. Engineer VERY MUCH on defense, much less on attack. Dont forget to sap everything you find.)
3.Sniper, Soldier, Pyro. (these are more situational. Soldier can be a pain in the ass when he is attacking. Pyro can completely airblast spam deny your push so picking him when your opposing team is about to lose a push could be a good idea if you're still alive at that point. Sniper is a VERY important pick and is often ignored way too much in lower leagues because of hes pub reputation. But sniper is probably the most dangerous pick class and should be focused down ALWAYS before a push happens.)
4. the rest. The spy and and the scout are picks you can get to help your pyro or flanks. Overall the more people are down on the enemy team the better but the pickorder is very important. Just think ''If I was them, what class going down would piss me off the most?'' and go for him.

As a spy you have a wide range of powerful revolvers in your use. And whether you base your entire gameplay on your revolver as a ''Gun spy'' or use it as a trusty sidekick in those sticky situation when noticed by the other team or just otherwise. You truly should find the revolver that suits you and the way you want to play the game.

1. The Revolver
First there is your trusty sidekick. The good old six-shooter ''The revolver''
Damage
Maximum ramp-up 150% 60
Base damage 100% 40
Maximum fall-off 50% 20
Point blank 55-60
Medium range 35-45
Long range 16-25
Critical 120
Mini-crit 54-81

Function times
Attack interval 0.58 s
Reload 1.16 s
Spread recovery 1.25 s

The revolver has the highest damage output of all the pistols one can use. This revolver is easier to handle than the ambassador and people have compared it to the scouts scattergun exept that every hit is a meatshot. Damage-wise this is the only revolver that is comparable to the Ambassador and in my opinion is the better choice because of the reliable damage. Easier aiming. and no need to wait for aim to reset before another big spike of damage. Takes some getting used to but far less than the ambassador. Overall A VERY solid choice for a revolver.

2. The Ambassador
Damage:
Maximum ramp-up 150% 51
Base damage 100% 34
Maximum fall-off 50% 17
Point blank 46-51
Medium range 31-37
Long range 15-19
Critical 102
Mini-crit 46-69

Function times:
Attack interval 0.696 s
Reload 1.16 s
Spread recovery 0.95 s

You either love or hate the 102. This gun is like the knife. A very pick-heavy weapon and can be used to a devestating effect by a skilled gun spy. or to a few crucial headshots by a knife spy. This is the revolver with statistically the 2nd highest dps of the revolvers. Takes A LOT of practice and getting used to though. (My recomendation is harvest or hightower.) Another solid revolver to use but if you cant get yourself to reliably headshot, or just want a more steady dps weapon you should go for the revolver instead.

3. l'etranger
Maximum ramp-up 150% 48
Base damage 100% 32
Maximum fall-off 50% 16
Point blank 44-48
Medium range 28-36
Long range 15-18
Critical 96
Mini-crit 43-65

Function times:
Attack interval 0.58 s
Reload 1.16 s
Spread recovery 1.25 s

The l'etranger is really a gun made for knifing. Shooting a target will give you more cloak. and this can really be paired up well with the deadringer and the increase of cloak from just having one is really good for invisibility watches. This gun can make you survive better than any other with the cost of A LOT of dps. I would never suggest taking this gun if you plan on playing gunspy. but if the map has a lot of areas where you need to cloak or is just a brilliant map for knifing anyways then go ahead and try it.

Im not going to include the diamondback or the enforcer here. The enforcer after ALL the nerfs is just a horrible ♥♥♥♥♥♥ version of the amby. And the diamondback, while being usefull in some situations doesnt fit the spy gamestyle. Since you'll most likely die when getting a pick so racking up the crits probably won't happen too often. Also it's banned in etf2l 6's for some reason...

The spy has a fine variety of knives, allowing for more passive or agressive play and defining what you can and cannot do.

A knife that you typically avoid in competitive is the Your Eteral Reward. It serves little purpose as most people on teams will be banded together.

A great knife for getting single picks and getting out is the Spy-Cicle. In competitve, the pyro does much more spychecking than in pubs. Try using the Spy-Cicle when you know your team can distract the enemy pyro long enough for you to pick off someone (most of the time will be the medic).
The Kunai allows for some really agressive play; that is, if you can get the first stab. 70 health is not a lot, many things can one-shot you. I only recommend using this knife in very cramped or crowded maps, as the massive overheal will help you assault and escape.
The Big Eaner. It's hard to describe this weapon. Now, a great combination with this is the Dead Ringer, allowing you to move as fast as a scout and be very hard to track down. Following its recent buff, I could see it being used in competitive, but cautiously. This knife is only if you feel confident in getting more than 1 kill in a life, and certainly causes paranoia.
Just like most classes, the stock knife will always be the best. It's not beneficial, nor detrimental. It's the perfect inbetween.

Trickstabs are something completely unique to the spy. No other class is going to jump over the enemy's head and instantly kill them.

Though, trickstabs in competitive, are literally the last stand. If you can't use your pistol, you can't cloak away, and/or they're too close to you, your knife is the best option.

If you do not know how to trickstab, you probably shouldn't be reading this guide. This guide is by no means for beginners, but for people who want something more than Valve Pubs.
Trickstabbing is an ancient thing to TF2, nothing new. But it has it's situations.
Take this situation for example: you're behind a rock, hiding from a heavy on the other side of it. He just got finished shooting and you know he's walking to you. You have the upper hand. If this rock is on a hill, you could walk around it, and do a stairstab. No desperation needed, and done correctly, they won't know what hit them.

Most important to trickstabbing: knowing the movement speed. I cannot tell you how much I messed up on a trickstab because of movement speed. There's a very obvious difference between how fast a heavy and how fast a scout moves, so treat trickstabbing them that way. Scouts will usually be jumping, so I do not recommend trickstabbing them.

Strafing plays as much of a part in spy as it does in Soldier. It's very important.

Strafing kind of goes along with trickstabbing, but not so much. You can do something called circle strafing that allows for some quick backstabs. Basically, let go of all buttons except A or D, and move your mouse at a steady pace in whichever direction will get you to their back. (A+Slide mouse steadily to the right.)

Keep in mind that, when strafing, you gain speed in the air. If you were to watch surfers do their thing, they're constantly strafing, gaining speed. Keep this in mind for dropstabs.

What really works with this is unpredictability. No matter what watch you're using, you can get out of sticky situations. (Much less often in competitive, but still very possible.) The dead ringer allows for some really agressive plays; remember to always jump after stabbing, and surf damage!

Strafing is a simple part to TF2, but very important for getting good at all of the classes, especially spy. I can't explain exactly how important strafing and constantly jumping is to spy (and in competitive), so really you'll just have to get in game and try it yourself.

Acting skills are what make the spy unique mostly. Being able to trickstab is good, and knowing when to use that revolver is amazing as well, but acting gives you the most advantage for both your team and against the enemy.

Now, believe it or not, it's possible to fool people with the scout disguise. Just as it is the demoman disguise, or the sniper.

Think logically when disguising. The pyro might want to reflect projectiles away from an engineer's sentry. Try that. Soldiers and Heavies are great disguises for grabbing the medic's attention, or even popping uber on you (oh that truly is a delight).

One thing I highly suggest is leaving one shot out of your revolver. When you reload under a disguise, your disguise reloads the weapon they're holding.

If you're disguised as a soldier with low health on the disguise, having this one shot out is amazing. Walk around a corner where the enemy medic, engineer, etc. are, start jumping around like a soldier trying not to be shot, press the R key and switch away before the revolver clip is fully reloaded. Such a godly technique.

What many spies say in their head is "back, must go to." All wrong. Spy is the most slow class, but not in terms of movement speed. You should be predicting where the enemy scout is going to be backpedalling, not where he's going to strafe to.

Like sniper, you (should) know where the enemy is going to be. You know there is a wounded scout, he's going for the health pack. Pull out your revolver.

Pyro saw you earlier? He's gonna be flaming around. Unpredictable; ABORT, ABORT!

Medic is wounded? The enemy is going to protect him. Act like a teammate, and slaughter the medic for the upper hand on the entire team.

Even though spy is a great class, and can deal massive amounts of damage in a single click, if not kill, decisions are narrowed to 3: Knife, Revolver, Cloak. This means should I, or am I, safe to cloak away? Should I go for a trickstab or take someone down with me? Should I shoot, am I in the correct position?

You are an important part of a team. You being dead is a large disadvantage to your team. Knowing when to pull out your revolver, knife, or cloak away is very important.

If you are on the front line with your team, you should be shooting. You're not doing anything with your knife, so shoot!

If you have time to get behind the enemy or get to your team, use your cloak.

If you feel confident that you're getting a stab, do it. Remember: never go for a stab directly; acting is important.

It's very important to choose who you want to pick. But most of the time, it's not who you want to pick or who you can pick, it's about who your team needs you to pick.

Some would say the Sniper is a free pick. And you know, I'd agree. But, they would also call out your position, who you were last seen as, etc.

In a decision between the Sniper or the Medic, the Medic wins the bet of highest value. So, don't give out your position and waste time going for the Sniper when you could have made the Medic drop Uber!

But don't forget, the Medic, though he is 99% of the time, isn't always the highest priority. Sometimes you should go try to pick the Demoman or Heavy if your sentry gun is keeping them held back. If you've got a good hold because of the sentry, don't just waste that, try to keep it alive!

Of course, you're not going instantly from a pub to UGC platinum, so pay attention.

First thing: TF2center.com. All you need is 300 hours and you are free to play in whatever game. Though, I urge you, read the rules on the first page.

If you don't have a microphone, perhaps you're not quite ready to play competitive. Competitive is very talkative, you're not gonna stop in the battlefield to type something out.

Finding a team is a hard thing to do. You're not often going to run in to people in valve pubs ready for highlander. So how do you do it? TF2pickup.net is a great place. Or you could just happen to run in to people and form a team. It's bound to happen eventually.

Spy is a great class, but there is by no means a lack of spies. If anything, there's a lack of medics, heavies. If you want to get into competitive and think spy is good for you, take a moment and go get good at every class, and really see what you favor.