It depends on what kind of environment you're playing in, but if you can, try to fake them out. Once you know where they're at, take cover and fire in their direction, then pause for a while, then fire some more. In the same length of pause, move quick and quiet and try to outflank them. Try to anticipate what route they'd take to try to move in on you or where they would hide to return fire to your previous position. When you move to flank, keep in mind where they were and where they're going to be and try to position yourself so you're either beside or behind them when you move in to finish the game.
I usually try to engage, move, hide, let them pass, then engage from behind.