As a player it's important to know your strengths and weaknesses. Honestly analyzing your strengths and deficiencies may be hard, but an honest self-assessment is half the battle.
Players have different strengths and weaknesses. While a player may have several strong skill sets, it's rare a player can be good at every aspect of the game. That said, some players are lightning quick, some have great hands (puck handling), some may be physically strong and effective playing the body, while others may have a heavy shot.
This applies to goalies as well, Some netminders may have a great glove hand, whereas others may have great rebound control. Again, the point being every player has some areas of their game that are strong (or weak) and playing to those strengths while limiting exposure to those areas of weaknesses will help them be more successful..
A great example of a player knowing their strengths as well as limitations is former Boston Bruin defenseman (current NY Islander) Zdeno Chara. Chara wisely recognized early in his career that skating and speed weren't his strengths, however his massive size (6'9") strength, and reach allowed him to successful by keeping opposing forwards on the permitter, win puck battles in the corner, and keep the crease clear for his goalies. Playing to his strengths allowed Chara to play 24 seasons (and counting) in the NHL. Had Chara decided to be stubborn and want to carry the puck all the time or think he could out skate everyone he would have failed. Instead he used his physical attributes, of size and strength to carve out a very valuable niche (being a "shutdown defender") for himself and his team.
Once identifying their individual strengths and weaknesses players can work in practices to reinforce their strengths but also improve those areas of weakness. Additionally, players should use this knowledge of their skill set to avoid putting themselves in situations where those areas of weakness can be exploited by opposing players.
As a coach one scenario that comes to mind is the speed/agility disparity. In far too many games over many years I have observed a slow-footed defenseman get burned by a speedy forward busting out of the defensive zone. In nearly every occasion this occurred because the defenseman either didn't recognize the speed advantage of his (or her) opponent, or wasn't honest with themselves about their own speed/agility limitations.
If the player, (or the player's coach identifies this limitation in the player, there should be a light that goes on in the player or coaches mind (using their HockeyIQ) that they need to be more careful when on the ice against a very speedy player or players. Maybe they use that recognition of the skill disparity to retreat more quickly from the offensive zone or be super careful about pinching down the wall to help counteract that speed disadvantage.
The above example is just one of a myriad of examples I could cite to illustrate how a player needs to be cognizant of their strengths (or weaknesses, but the trick is for the player to understand their game and then adjust their playing style to put themselves in the best position to succeed.
The more a player understands themselves, their opponent, and uses their HockeyIQ to play better strategically the more they'll enjoy the game and the bigger impact they'll have on it ... regardless of the skill set they possess.