You will survive longer in the game if you get yourself to the nearest rooftop of a tall building. Find a ladder and climb all the way to the top. Then go prone and start sniping from the edge of roof. Be sure however to withdraw from edge and move to another Location after firing a few shots. Fire from another position on the roof. The AI controlled enemy cannot climb up the ladders To come after you. I guess they're not smart or brave enough to do so. However they can still look up and shoot at you so be Careful. Also if they try to throw a grenade at you it will not reach you on the roof.
be a spec ops and take your C4 and place them on the hood of a humvee, buggy, or any other vehicle and go to your detonator. drive up to the tank and stop to get out. the tank will stop and turn. use this time to run away and detonate the C4.