Self defense begins way before any physical altercation. Violence must always be a last resort. Not just because of moral obligation, but practicality. A violent altercation can lead to serious injury or death. Then there are the legal ramifications. There are lots of things you can do to make sure things don't escalate to that point. Here are some ways to avoid a trip to the hospital or central booking.
1) Trust your gut. While many of our fears manifest as anxiety based on irrational thoughts, this doesn't mean we should ignore instincts of impending danger. Having a "bad feeling" about a person or place can at least help keep you more aware. That can make all the difference in your reaction time if something does break out.
2) Face the entrance. My brother, an NYPD cop, told me when he first got on the job to never sit with my back to the door. That has stuck with me for nearly twenty years. One of the worst things you can do in martial arts is turn your back to your opponent. You can't see what's happening. You are open to being choked or struck from behind. Virtually defenseless. Knowing who is coming in an out will allow you to spot any potential danger quickly.
3) Have an exit strategy. The goal of self defense is to get you home safe. How do you get out when something pops off? Are there any potential obstacles in your way? Is there a back up route? A quick assessment of all your ways out is like a mental fire drill that can make an evacuation much smoother.
4) Know that you're gonna be afraid. Adrenaline can be a killer if you're not used to it. Managing internal reactions to fear is a major reason I encourage my students to compete. In a self defense situation, there is obviously much more on the line than a medal. Practicing keeping your cool in stressful situations and confronting some of your longstanding fears can give you confidence and help you take more control of your inner reactions.
5) When all else fails, fight dirty. When violence is necessary, rules and fairness are out the window. If a person wishes to do you or your loved one harm, you must be able to flip a switch that turns you from a sweetheart to a rabid animal. Everything from weapons, eye gouges and headbutts to biting down on flesh (the last, last resort) are things that you must ALLOW yourself to do. Reality is not about points. You must fight to win because your life may be at stake.
While it's easy to believe the world is more dangerous than ever, history shows us that isn't the case. That doesn't mean you shouldn't be prepared to mentally and physically deal with a dangerous situation. At the very least, it will give you the peace of mind that can make your world seem a little safer.