If you captain a team, do not: 1.) let a player insist they play first every week.
2.) have a player ever fail to play for more than two league nights in a row.
3.) let a player get in the habit of not paying for his/her match on league night.
4.) let a player (especially a low-skilled one) tell you that they do not want you to call time outs on them.
5.) let/insist a player sandbag.
Do this as captain: 1.) have/teach all teammates to keep score.
2.) let someone (especially a working person) know as soon as possible if that person won't be playing on any given night so they may go home at a decent hour.
3.) make sure your teammates understand the rules and play fairly and honestly by them.
4.) have your players practice good sportsmanship.
5.) make sure your teammates understand that winning an APA league match is not akin to winning the U.S. Open and act with accordingly after winning.
There is probably many I am missing, but this is a good start. You'll figure it out a lot quicker than you think you will.
All of this.
Some additional thoughts... Learn whether or not "playing up" or "playing down" bothers certain players on your team. Explain to them that many times it's unavoidable, but having it in the back of your mind allows you to put your players in the best possible situation. (If they go into a match already uncomfortable because of playing up/down, it won't help.)
Believe it or not, find out if your player has a block against playing ladies, particularly older men. (I have one guy on my team that subconsciously plays worse against ladies. He's not an ogre, just let's down some) That doesnt stop us from playing him against ladies, it is just another variable we use when deciding on matchups. All this stuff is a part of getting to know your players. There are likely many other quirks to be aware of.
I try and look at the roster of my opponents team before arriving at the pool room, and to have a basic idea of who I want to play. You can't be married to any plans, but if you have an idea going in, it takes less time to make a decision. Once I arrive, I immediately start to try and see how many of my opponents team are present, since that can affect who they throw. Obviously, players can arrive as the evening goes on, but if a particular player isn't present, that can affect your strategy.
Encourage your players to load the APA app on their phones and to create an account. Often they can get answers to many questions on their own there. They can see schedules, etc. And the rule book is available there, for everyone.
I'm sure there are a lot more things that I'll think of later.
Most importantly, try to insure that everyone knows its supposed to be fun. Yes, we can all be unhappy with our own performances, but we should all be having fun, playing pool, and enjoying the time there. If you're not having fun, why on earth would you spend the time and money? Construct your team with that in mind. If you have to deal with people who take away "the fun", then it becomes work, for all involved.