So true... as an engineer on some maps I'm lucky to go 1:10
If your team wins, and you contributed to that win, who cares what your ratio was...
Got to agree with G & Z. Stats are ...meeh... just play for objectives and FUN. Playing as allied engineer (on pubs) is the surest way to get 1:5-10 ratio. But however , if you are concerned about your ratios then play as axis medic or Mortar.
Don't run out in the open if you can help it for too long. Always be thinking where the enemy will come from (spawn, objective) and adapt your surroundings to help you in this.
Learn when to reload. Don't go reloading and / or moving in places where people could appear from round a corner and score 3 easy headshots. Adapt to use the pistol and practice getting headshots. Turn auto reload off.
You may want to turn hitsounds off if you play with them on.
Don't use nades much, especially not if you're a medic. For a certain amount of time you can't shoot or revive, and if you don't have a good sens you can end up doing damage to yourself if an enemy suddenly appears near you.
Be aware of sound: Listen for others and recognise that others can track you by your own noise. Crouching+walking = no noise.
Don't crouch+prone too much in firefights (imo). The more consistant you can play the game the better...you're obviously adjusting less. Despite what people think, if you've a decent aim you should still get the same sort of accuracy running as crouching, and you're moving faster. nb: the hitbox of a crouching pistol player gives an advantage, but pistol really needs speed.
Get in the habit of returning to head height level with your crosshair, after you've done stuff like looking up / down, jumping etc.
But just in general, play more, gather experience and all the while predict what is going to happen ... from small things such as turning into corners before you reach them, to being able to deal with 3 or 4 people coming out of a known area, like the spawn.
Oh ya, and knowing the enemy's spawntime is useful. You only need to witness them spawn once.
Axis spawn every 30 seconds (default) So if you saw them spawn on 34 seconds, they would also spawn on 4.
Allies spawn every 20 seconds (default) Likewise, a spawn of 34 would also mean they spawn on 14 and 54.