Probably one of the most important things to do as a lacrosse coach is to make sure that all of your players have legal sticks.  They must be more than 40" long, without a bent handle, with a legal depth pocket, without a pinched or otherwise altered head. This can also be far more difficult than you might imagine. They change handles, etc. all the time. Heads are different lengths, etc. Things can go south in a hurry when your team had a stick that was too short and is slapped with a three-minute penalty with no release no matter how many goals the other side scores. Don't ever let this rule beat you.

Get a rule book. Read it cover to cover a couple of times. This is a way that you can powerfully help your team. Knowing the rules as a coach gives you tremendous confidence, as well as opening your mind to ideas that may at times seem insightful or even brilliant, simply because you really understand a certain rule.

I think it is a good idea to skim the book the night before a game. It's amazing how often that some rule you may have focused on the night before that seems obscure will come into play during the game. Do not memorize the rule book, just learn the rules.

One of my pet peeves is being off-sides. I am constantly amazed at how often the highest caliber teams can get two or three off-sides calls in a game, even without the other team trying to bait them into going off-sides. All you need to know is that four guys need to be on the defensive half of the field and three have to be on the offensive half of the field at all times. When a goalie, attackman or defenseman wants to leave his side of the field, a middie needs to stay back for him. Have all your middies help to make sure that one of them is always back. This is at the heart of team play and teamwork. Teach it from day one.