A great actor and martial artist once espoused emotional content in blows. This gives the mind and body a connection, an urgency, a commitment to its movements.
Also espoused was the "two-inch punch". I advocate something similar, what I call a straight punch, punching ahead while facing an opponent, putting body weight into the blow. While a hay-maker can be delivered by surprise from outside the opponents peripheral vision, a straight punch comes fast from a poised fist, with the hips, back, and the entirety of the arm musculature poised. It comes fast, is the key, with no sustained wind-up like a hay-maker.
The man relying on the straight punch can deliver at least one blow before the man with the hay-maker has even committed his body to his own punch, and this thusly is surprise.
In defensive posture, the body must become as water and bend to the blows rained upon it, absorbing and moving in the same direction as the fists or feet to nullify force. Do not tense your muscles to prove your toughness. You will have bruises if you do that. Be as water, envisioning in your mind a splash will blows come.
You do a "ready to grab" pose, with hands about belt high, hip high, poised so as to perhaps play a piano, with palms down, slight space between the fingers. To slap away a blow is acceptable from this position, but there would be little force behind a slap landed as an offensive blow; no damage is done in slapping, but rather that slaps PUSH the opponents appendages away.
The feet and hands must have quickness. Catch chickens like Rocky Balboa in that movie; it will develop a quickness, a greater dexterity in motor control. Slip the jab; slip the jab. Disguise a heavy, bruising jab as a half-hearted blow with no emotional content, and your enemy will wonder what hit him.