Vigilance, Prepared Reaction
Malicious events happen rapidly. Often a strike comes from your blind spot or when you are not paying attention. Other times a close-range fight of attrition may leave you no choice but to absorb dangerous blows. Vigilance is therefore the top skill to master, providing early threat detection. Physical vigilance identifies unusual movements, glimpsed weapons, and risky situations. Psychological vigilance reads mental states from speech and body language.
Once you detect a threat, you need to react quickly by having a plan prepared beforehand. A list of general prepared reactions can save you precious seconds of time during a high-risk situation. Your general options are to escape, defuse, or fight. If the threat is a risk to someone else, you may have the luxury to observe the scene while repositioning yourself appropriately. More specifically, you can prepare different stances and default blocks against punches, knife thrusts, bat swings, and gunshots. For example, a novice right-handed shooter will flinch to their bottom-left, so sudden defensive movements to their right side can be very effective; at the start of such an engagement, you can rotate backwards clockwise into an angled right-handed stance as a split-second evasive maneuver to reduce your target size and protect your liver.
Start with absolute safety, including eye protection, ear protection, contained firearm transportation, muzzle control, barrel checking, situational awareness, proper grip, proper slide operation, proper magazine insertion/ejection.