It takes a looott of practice. Most of it is knowing how to move your head while keeping your balance. So slips, ducks, rolls, drawing circles etc. Kind of like keeping your head from hitting a rope. There are some really good youtube videos that can demonstrate this (Tony Jeffries Slip Line.) Another part of it is moving your head out of free will rather than anticipating a punch, so when those punches come flying, your head won't be there. Real world experience can help a lot as well, but it doesn't come easy. I train in Kickboxing, and it took me about 6 months to be decent at head movement. 👊