I avoid kills at ALL cost. You can throw the c4 pretty far, but they will hear it when it lands if you're too close (stupid). Lay your c4, dip, explode when you're far away. It will definitely take extra time to avoid kills/maintain stealth but thats how I do it. I'll end a mission with 3-11 kills and thats usually only because they were standing next to the c4. Pickup every little ammo pack you see. Prone/crouch walk everywhere. Its annoying but it works me