How do I learn not to get hit?

Everybody pictures defense as fast reflexes, ducking and weaving. That is the last layer, not the first. It gets built in this order:

• Distance. Not in range, nothing lands. Footwork is defense, and it is the layer that costs you nothing.
• Position. Chin down, hands up, elbows in. A real guard means the shots that do land hit glove and forearm instead of jaw.
• Interruption. A jab in the face of somebody stepping in stops more punches than any slip ever will. Hitting first is defense.
• Movement. Slips, rolls, pulls. Last, because they only work when your feet and your guard are already honest.

New people get it exactly backwards. They stand flat in range with their hands down and try to be quick. Quick does not save you at the wrong distance.

Here is the encouraging part. Nearly all of that trains without anybody hitting you. Footwork drills, mitt rounds where the pad comes back at you, me tapping you with a soft pad every time a hand drops. Plenty of people I work with never take a real shot at all. The interruption layer is the one they skip, and it is the most useful thing in boxing: the jab.

There is one range where none of this applies: when they have hold of you and you are both still standing. Distance is gone and head movement does nothing. What the clinch is covers it, starting with how to get out.

Staying calm with something genuinely coming at you does eventually need light contact. When you want it, it starts slow, with gear on, and you set the level: will I have to get hit.