Snipers are popular classes in any shooter game, but Snipers in Team Fortress 2 work very differently from what is expected. For one, the class's damage output is significantly less when unscoped. Another difference is that they don't do huge armor-piercing damage like traditional FPS Snipers unless they are scoped headshots. There's a lot of other things that make the TF2 Sniper different from a traditional FPS sniper.
Because of this, both new and seasoned FPS players make a lot of mistakes as a TF2 Sniper. There's no other learning curve that can make one good at being a TF2 Sniper other than playing as him. Call Of Duty won't help with learning TF2 Sniper mechanics. Battlefield won't, Arma 3 won't, and Overwatch won't. Here are the common mistakes players do as a TF2 Sniper.
10 Overusing the SMG
In any other game, a submachine gun is an effective close-quarter combat weapon that can quickly just about anyone. In TF2, however, it's merely used to finish off low health enemies, as the Sniper's SMG does a maximum of 12 damage per shot. The mistake most new players make is going about trying to kill enemies with it. A TF2 Sniper's primary is more reliable in doing damage.
When dealing with enemies close-quarters, a Sniper should develop the skill to quickly scope in and headshot an enemy. Only after the headshot can the Sniper finish him off with the SMG. Also, a Sniper should have the confidence to use his melee in close-quarter engagements.
9 Standing Still
The Sniper is the class in TF2 that requires the most focus. Newer Snipers would be too zoned in with their scoped sights that they would even forget to move about. Standing still makes the Sniper an easier threat to rival Snipers, Rocket Jumping Soldiers, Spies, and, in some cases, taunt killers.
A good rule to follow is to strafe about after every shot taken. Spies are more likely to miss a backstab on an erratically moving Sniper. Adding to this, Snipers shouldn't nest in just one area. Good Snipers will occasionally change locations, thus adding to their unpredictability.
8 Not Looking Around
A Sniper is a Spy's natural prey. A lot of Snipers tend to focus too much on what's their scope that they forget to look around at what's obscured from it. A good rule to follow besides moving and strafing after every shot taken is to look around as well as listen if there are players getting killed outside of the Sniper's focused field of view.
A little environmental awareness, paired with some anticipation scoping, can protect the Sniper from impending threats. A Sniper, upon seeing or hearing that an enemy is coming up to him, should quickly re-orient his scope to the hallway that leads to his nest.
7 Showing the Laser Pointer
For the enemy team, the laser pointer is a good indicator that an area is under Sniper reconnaissance. Snipers are assassins. They're supposed to be undetected and deadly. The sight of an enemy team-colored dot on the wall will discourage flankers from passing through the area containing it.
Additionally, the dot can be traced back to the Sniper; revealing his nest. A good rule to follow is to hide the dot. Obscure it on the frame of a passage so enemies passing will not see it at all.
6 Undervaluing Body Shots
Though new Snipers are expected to make a lot of mistakes, skilled Snipers make one very common mistake: they undervalue body shots to such an extent that, when an enemy sees that he's been killed by a non-headshot, he would taunt the Sniper for being "unskilled."
Headshots can instantly kill lower-health classes like Scouts and Medics. For classes with higher health like Soldiers or Heavies, however, there's no shame in going for a body shot to finish them off if the headshot doesn't kill them. Targetting the chest versus targeting the head will both result in red health enemies being killed. The smart option is to go for the easier target and hit the body shot.
5 Wrong Target Priority
An effective Sniper will decide which key targets he's supposed to take out first that will make his team's push much easier. If a Sniper is also on the opposing team, he should be taken out first. Next, if a Medic and Heavy duo are harassing the team, the Sniper should take out the Medic first.
The late Medic's patient should be targeted next after killing the Medic. First priority targets are Rival Snipers, then Medics and Engineers, and then area-denial classes like Heavy, Soldier, and Demoman. Additionally, a Sniper should pick off anyone outside the effective range of his team.
4 Improper Loadout
A Sniper's playstyle has a lot of approaches given that he has a ton of different weapons. With the Hunstman bow and arrow, he can adopt an offensive playstyle and even engage near the frontlines. With the Sydney Sleeper, he can take the role of a support, coating enemies with a Jarate's debuff from a distance. With the Machina, he takes a crowd-control role with the weapon's piercing ability.
Sniper's secondaries, as well, are various, as are his melee options. Knowing what each weapon does and deciding what they're good for is an essential tip to playing Sniper. Very common loadout mistakes include wearing the Razorback when there are no Spies, using the Machina when there's no choke point in the map, or using the Bushwacka without any mini-crit buffing weapons.
3 Underestimating Close-Range Effectiveness
Though the Sniper is obviously a long-range mercenary, he's not too bad in close range either. This underestimation of his close-range lethality leads the Sniper to make some overly conservative approaches.
With the Huntsman, a Sniper can instantly kill a full-health Heavy with a quickly charged shot. With the Jarate and Bushwacka combo, a Sniper can clean house with criticals galore. And, in the hands of an expert, a Sniper can quick-scope adversaries near and far, allowing him to push the cart with his team.
2 Pulling the Huntsman Bow Too Long
The Huntsman is a Sniper's solid choice for flexible offense. A fully charged shot can deal huge amounts of damage. But, pulling the string for too long will cause the arrow to misfire. An indicator that the Huntsman has already been pulled too long is that the weapon begins to shake from the tension. When fired, it won't fire directly forward.
A Huntsman should never be drawn longer than five seconds. A Sniper without a target should lower the Huntsman once it's pulled back for too long. This can be done with right-click. Alternatively, a Sniper can quickly switch weapons, and then back to his primary.
1 Wearing Unusuals
Wearing unusuals is a nice way to show off one's wealth in-game. They're extremely rare cosmetics with moving/glowing particles and effects.
However, as pretty as they look, these bright effects are as visible as a road warning sign. As a Sniper, it's best to stay hidden and not to draw too much attention to himself. Unusual cosmetics make a Sniper much easier to spot even from afar. This could result in a rival Sniper getting the upper hand on him, and the opposing team to be cautious of his presence.