reaction timing. play pve missions with lots of enemies or heroic strikes - and play like you are a goddamned hero of the human race. play like you are invincible and try not to die at the same time for as long as possible. it helps you react quicker to sliding shotguns, blink strikes, when you see a red glare from a sniper, things like that. also, crimson doubles is good training for trials, because you pretty much have to get the res. ALWAYS GET THE RES.