If you are in a self defence situation you only have a few seconds to decide how to bet defend yourself. Easier said than done but the first rule is to try and relax and stay focused. This will help to conserve energy which you may need. If you must physically defend yourself there is no time to be civil it is hurt or be hurt.
The most affective parts of the body you should aim for and can damage most easily are: the eyes, nose, ears, neck, groin, knee and legs.
Weapons: By which I mean your physical built in weapons. Use elbows, knees and head. These can be used most effectively for inflicting damage.
At ECKA we practice contact to get you used to the feeling of being hit (all at a safe level) as this will help reduce your freeze time compared to someone who is not used to be regularly hit. Your freeze time can be the difference between you defending yourself successfully or not. It also helps you develop awareness of situations and your options to escape or defend.