Basic Block - Double Guard (hands)
For the fastest, easiest, when in doubt defense, place your hands on your temples to protect as much target surface area as possible. Keep enough opening so that you can see through the gloves.
Basic Duck (head)
The fastest and easiest head movement is to simply bend your hips and knees to change your level. Keep your hands high, and your eyes on your opponent (you can look just above their belt line instead of their collarbone/chest)
Basic Step Back (feet)
The fastest and easiest foot defense is to simply step straight back. Notice how your Ready Position does not change, maintaining optional next defense or offense.