How can I aim better/kill people more often in first person shooters?
It depends on the game of course but here are some rules that you may find helpful:
Don't spray, make every bullet count.
For shotguns and sniper rifles it means that must be confident that you are going to hit your enemy when you shoot. At first it might become even harder to kill someone but it's a proper way to improve your aim.
For assault rifles it means that (again, depends on the game) you should shoot in short bursts making a tiny half-second breaks to decrease the spread.
Learn shooting techniques like drag-shot or twitch-shot
A good mouse and mouse sensitivity that suits you. I think majority (debatable I guess...) of professional gamers use rather low mouse sensitivity. They use the whole arm and the whole mouse carpet to turn 180 and use their wrist for precise movement. It is also important to have enough space to move your mouse. I feel extremely uncomfortable when there is something fragile on the same table where I sit...
Turn off mouse acceleration. Everywhere: in mouse drivers, in OS settings, in the game. Most people agree that it helps but there are a few guys who like to have it on.
Turn off vertical synchronization, tune your network settings. For source games cl_interp, cl_updaterate, cl_cmdrate etc can make a difference.
This is entirely dependent on the game, but learn whether your guns are hitscan or projectile.
Hitscan weapons have their bullets travel instantly; a hit or miss is calculated as soon as you pull the trigger. Don't rely on visual feedback alone to determine if a weapon is hitscan -- depending on how the bullets are animated, they may appear to be slower than they really are. The most important thing here is that you shouldn't lead with Hitscan weapons, as doing so will only make you miss.
Projectile weapons, on the other hand, have actual projectiles that need to hit the target to do damage, so you do want to lead your shots.
Take the time to practice all of these things by yourself, in a practice game or against bots
- Mindset - protect yourself first and be unaffected by enemy gunshots
- Control - every movement in battle needs to be deliberate, and perfectly executed
- Take Cover - a single mistake here will cost you your life
- Dodge Bullets - know how to sprint from cover to cover, with the right timing
- Aim and Shoot - specific strategies to improve your aim (covered in video extensively)
- Kill Entire Squads - practice your skills in a live situation against multiple enemies
REMEMBER: where is the enemy? how many are there? do i have good cover? can they see me? will i get hit? where am i looking? 360 degrees? or tunnel vision? can i get a shot in? shoot to scare or kill?
position, safety, and awareness is infinitely more important than trying to "kill someone before they can kill you" - a common mistake to make especially if you are not thinking clearly
I made a video series with some serious tactical and training/practicing strategies to help you get better at shooting games. It's a 4-part training series about an hour in total.
This one is probably what you're most interested in...
Part 2: (practicing strategies)
If you like that video you should watch the rest because they will help you even more.