When playing as a Predator, select your shoulder cannon then charge a shot by
holding the Right Mouse Button. This will consume a small amount of energy, 
but you can recharge it by pressing T. After that, the game automatically 
returns to the shoulder cannon. Notice that the shot is still loaded, and 
causes a lot of damage. Go to the Queen at a safe distance with electric 
view and fire. Then, just keep moving in circles walking backwards and 
shooting without charging the shoulder cannon. When your energy is out, use
the spear weapon to finish it. A few blows should do the trick. After that,
kill the other aliens that appear then move to her head. Use your blades 
and keep attacking the head. It will increase your trophy number.