Here are a couple ways to do this.

Change audio to war tapes, it makes everything sound clear so you can hear everything around you.

Listen for enemies, they always make noise, walking, throwing grenades, reloading, when shot, when teammate is killed, knifing, dies, almost everything gives away there location you just need to figure out from which location.

Find ways to get around, there are countless ways to get around finding ways to out smart your opponent will give you an upper hand in a match.

Use common sense, always assume your opponent can see you sneak around, avoid open areas, don't use the same route often, look around and through areas.

Pick your fights, taking on multiple enemies will most likely get you killed, if needed take one can change position for next target for they will have figured out where you are.

Spot enemies, pressing select or back puts a red triangle telling your team where the enemy is, it also works on your squad letting them know you need health ammo a ride or to attack/defend an objective.

Pick up kits, its a good way to help yourself and others, you can kill an assault to take his kit and give your team ammo or a medic to revive your team then switch back, take out an engineer and use his kit to repair or destroy a tank, grab a recon and use his motion sensors to find enemies or call a mortar strike just take what you need

Everything else depends on your skills and reflects, look and listen, slow and steady wins the race, ad for you run and guns out there i often go through windows i ever stay in one spot, like i'll hear someone upstairs i'll throw a grenade up and try to find another way to see up like a house next door or if im upstairs i'll throw a grenade down and go out the window and come around

with that said i'm LezzSamurai on PS3