When you are aiming to put on a fierce pose, it is a good time to conjure a memory of something that made you really angry. Try to recall a time when you were betrayed by someone you trusted blindly, or the time when you had to face injustice. You can also try thinking of a person whom you really hate, as that would automatically fill up your body with the emotion that you feel towards that person, hatred. Is your boss making life hard for you at office? Are your colleagues harassing you? Are you a prime target for the bully in your school? Is the girl you love head over heels for the football jockey? Think about these things.
With your mind full of angry thoughts, set your jaw by biting down on the back teeth. This will make your jaw line look really strong. Make the cheekbones become more prominent by sucking in your cheeks. You will notice your lips becoming thinner. Let it stay that way.
After you are done setting your jaw, it is time to work on your eyes. Narrow them to give them a menacing look and raise your eyebrows slightly. Let the angry thoughts and memories you conjured in the first step affect your eyes, making them look fiery and expressive of the emotion that is currently filling up your head.
Square your shoulders and lower your chin, though just slightly, while facing the camera head-on. Emphasise the muscles in your shoulders, chest and arms by pushing your shoulders down.
Hold the look while the photos are being taken. Do not let any happy thought creep in your head as it will ruin the expression on your face.