That's one of the biggest problems we have with beginners. They tend to close in and smother their own punches, and of course open themselves up. Then the opposite problem is staying out to far and 'reaching off balance' to deliver a punch. One of the early training techniques I use (beyond bag work) is to have an experienced fighter (padded up and instructed to deliver light punches), stand in a square 4ft X 4ft, (box is marked by tape on the floor). The novice is instructed to to move in and out, around, whatever, and try to deliver puches, combinations, --but understanding that the fighter has to stay in the box, but can block and punch back. After awhile, it accomplishes teaching the novice how to recognize his range, how to evaluate the range of the opponent, respect for balance and footwork, and it gives him some confidence. Now, later on, you can expand the box, and make the sparring as versitle as you want. I learned this from a fighter who trained in the early 1900's.