It sounds like you struggle more against aggressive players? For them to 2 tap they have to land 2 headshots, you have to make it as hard as possible for them to land the shot. Try not to get caught flat footed but if you do make your movements as random as possible. Strafe left and right but not equal amounts, through in a teabag strafe as well. Teabag strafe is when your strafing left and right but also pressing crouch repeatedly. It's tricky but effective. You'll either need to learn how to claw or switch crouch to one of your bumper buttons. I'm assuming you don't have the fancy Xbox controller which the paddles underneath? Make use of vertical space as well, learn to jump and shoot, primary's have more in air accuracy then secondary's, so if you switch to your sidearm your better off on the ground, if that's the case slide. It's all about not giving them a clear shot at your head. Be aware of the map, know where cover is so you can dip behind it, also where flat walls are so you can land a lightning/spike grenade to soften them up of finish them off. But remember they can do the same for you. Basically remember a moving object is harder to hit so keep moving as fast as you can, jump, slide, shadestep or twilight. I take it you know how to Titan skate, Warlock surf and do the Hunter head bang?