Hesitation is the enemy
Hockey is a game of movement and instant decisions. Generally speaking, if a player has two choices, and hesitates, he will fail no matter which choice he selects. On the other hand, if a player chooses either course of action quickly, he will often have a good result either way. Let's look at an example of this principal.
Assume the opponent is breaking out, and the defenseman can't decide if he should rush in (holding the point), or go back and play defense. If the defenseman hesitates too long, all is lost with either option. The opponent will be around him and on the way to a breakaway. Contrarily, if the defenseman immediately does either, he would probably have prevented the breakaway. Hesitation and indecision is the enemy. How can we teach the players to make a quick decision? Some ideas:
Identify those areas that appear to be a choice, but are not really a choice. For example, if there is a 2 on 1 break, and the defenseman covers the player with the puck, there really isn't a "choice" to "pass or shoot". There is only one choice, and that is to pass to the open player. In this example, you eliminate the hesitation by eliminating the choice. On a 2 on 1, if you are the guy carrying the puck, if the defenseman comes to you, pass. If he doesn't then shoot.
There are many other situations where either choice "A" or "B" are about equal, such as the choice for a defenseman to hold the point or go back and play defense. We cannot coach this as "always hold the point" or "always go back". What I tell my players is, "do whatever you are going to do, but do it immediately, because either one will usually work if you don't hesitate".
Lastly, and most important, never yell at the player for making the wrong choice. When players are afraid of getting yelled at for their choices, they almost always hesitate. After the hesitation, it probably isn't going to matter if they choose A or B, either one is a loser at that point. Some coaches seem to think, "if I yell loud about that mistake, the next time he won't make that mistake again". The reality is, "if you yell loud about that mistake, the next time the player will hesitate and not do anything, which is probably worse than the mistake".