Stand up for yourself! It is important that you stand firm in order to withstand the occassional hit and that you stand flexible for agility.
Let’s look at the basic position. Stand 45° sideways with your left foot to the front and your right to the back if you are right-handed. Right to the front and left to the back for the lefties among you. Feet should be about hip-width apart. You may bend your knees a little for a more balanced stance.
This position will give you leverage for your moves. Much of the force in boxing is actually created by hip rotation. We come to that part later.
Raise both your hands to your cheeks to form your guard. Make sure not to open your elbows too much. They should be close together to protect your trunk.
Your chin area is a very sensitive part. A knock there could really knock you out. Instead of looking straight ahead, bend your head, thus lowering your chin towards your chest. This minimizes the contact surface.
Now, relax and bounce if you are comfortable. You definitely look like a fighter and are good to make your first move.