-When you see an enemy, shoot a couple bullets at them. They will then come towards you, trying to kill you. Stay where you are and quickly equip yourself with a sword. Just before they reach you, quickly jump out and start hacking them with your sword (right clicking recommended). They will be too stunned to effectively hit you, and you can get an easy kill.
-When starting the game, hide behind a wall where your enemy cannot see you, but you can still see them on your screen. Throw a grenade not far from you, then hide behind the wall again. When they move towards you, and are just a couple steps away, jump out again and attack them with your sword.