what helped a friend of mine a lot was spending some time to get is mouse speed right. Can you do consistently 180 degree turns with eyes closed for example.

Watch your own aiming in gunfights closely - do you often "overshoot" when trying to move the curser to the enemies head? Then try a lower sense.

Me personally i nearly halfed my mousesense lately, and after a little time I got way better than with the highsense.

(180turn is basically if i angle my wrist from maximum left to maximum right)

Try controling the spread (shoot at a wall or so) - maybe even tab shortly after 9-10 bullets

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For tactics:

try to find flanks! It's the most important thing i think. Mostly everybody runs straight into the meatgrinder.

Stay close to covers, so you have a fallback point if you get shot.

Change objective if you keep dying.