What are the characteristics of a good defenseman?
A good defenseman is mobile on his skates, handles the puck well, makes good passes, reads the ice well, uses his stick well, and is a strong defensive one-on-one player.

Why are good defensemen such valuable components to their team?
Good defensemen are critical to their team¹s success because they are the primary line of defense and the beginning of the team¹s offense. If a
defenseman cannot effectively halt the opponent¹s attack, your team will be fishing a lot of pucks out of your net. At the same time, if a defenseman cannot make that first pass to get his team moving up ice you¹re going to be spending a lot of time in your defensive zone.

How do I become a good defenseman?
One becomes a good defensemen by learning and building the proper skills and by understanding and executing the proper positional techniques and systems that create a strong defenseman. 

What are the proper skills a defenseman must have to be effective?
I believe a defenseman¹s most valuable skill is his ability to pass the puck, both as a skill in-and-of itself, and also as a conceptual part of the game (see next paragraph). Any defenseman that cannot make a good firm pass is of little use to his team. Along with passing skills, a good defensemen must be able to handle the puck in tight spaces, allowing oneself the ability to create the opening to make a pass. Also, a good defenseman must learn how to use his stick effectively when not in possession of the puck. Lastly, a good defenseman has strong skating skills including forward and backward quickness, speed and agility.

What are the proper concepts a defenseman must learn to be effective?
A defensemen must be able to evaluate the entire ice surface from both an offensive and defensive standpoint, in all three zones of the ice. He has to be able to read offensive rushes and determine when is the appropriate time to join the rush. With the puck, a defenseman must be able to handle the puck under pressure, in critical areas of the ice, and possess the confidence and poise to find and get the puck to the open forward.
Defensively, he has to read situations and determine when to retreat, how quickly to retreat, how to control and create the proper gap, how to read the rush (is it an even-, outnumbered-, or superior-numbered rush?), and how to defend a one-on-one in all areas of the ice.