In as much as an attack will most likely catch you unawares, you should learn to think fast and make the best decisions as far as the best technique to handle the attacker goes. It is one thing to select a move and a perfect spot, but the way you throw the strike can make an impact in how effective it turns out to be in giving you advantage over your attacker. In essence, every self-defense technique or combination you select should actually work in reality and remain safe for you. How then do you evaluate what technique is effective enough when you need to save yourself from a situation?
It should be realistic. Not all martial arts techniques will always work when you are tackling human being when you are threatened or being attacked. Some moves are only best left to the training part and to keep you flexible and not in countering a real attack. It is best that you stick to techniques that have been tested and proven to work with uncooperative and fully resistant opponents so you do not end up compromising your efforts. Choose only what you know will work and not what you feel you should test out.
It should be safe for you. Remember when you get attacked you are not ready for a fight. This means that you will not have any protective gear as it would be the case when you are getting trained in a martial arts school. When attempting to apply a technique therefore, think about how effective it will be in injuring your opponent without causing you damage. Because you will be applying it with full power without any gear to protect you, think about how to safely apply and still yield the results that you are after.
It should limit the options of the attacker. When defending yourself from an attack, your biggest aim should be to render the opponent helpless even for a few seconds so you can run to safety. The technique that you select therefore should be good enough to limit ability of the attacker to counter attack or simultaneously hit you. It is best that you always go for a combination of blocking, parrying, footwork and covering so you are able to limit the options of your attacker. When you do not offer any position or distance advantage, you will be able to maximize your efforts.
It should do maximum damage. When defending yourself, the technique you select should be good enough to stop the opponent even just for a moment so you can get away. It should therefore maximize damage when targeted to the key areas. Try breaks, chokes, hacks, knees and elbows as most effective in causing injury.
A physical attack can be a matter of life and death. It helps to have a few effective self-defense techniques under your sleeve to use when the situation arises.