'Hit the other fellow, as quickly as you can, as hard as you can, where it hurts him most, when he ain't lookin'.
be careful not to slap. Many people land a hook and think they scored, but the judges won't count it because it landed on the inside of the glove, not the white part. This is a common mistake, and often people think they got robbed, not realizing that half the punches they landed weren't counted.
Try to relax. It will help your breathing and overall feeling. Keep your hands glued to your head if your are taking shots to keep your noggin from bouncing around in your guard. If he starts to flurry on you, tie him up or push him away. Mind your footwork and stay on balance and in position. Don't throw the same combination over and over. Try feinting the jab then stepping into a straight right to the body and a left hook upstairs, follow with a right uppercut as you are stepping out to his right side.