[tomegun]

Dave Libbey once described officiating at two games: on-ball and off-ball. You want to see the consequences of the ball while officiating a play on-ball. While officiating off-ball call contact. Period.
Another official mentioned the term "ref the defense" and said it was wrong. We should ref the matchup. Most of the time you will only have to look at two matchups (4 players) max at the C. Once it is more then that a rotation should occur.
Screening is one call that we have the luxury of being slow on. See what happens and then call it or no-call it. Often officials see a little bit of contact and pass on it. If Reggie Miller's teammates could set illegal screens with a tiny bit of contact Reggie would have a field day. Shooters only need an additional split second to get their shot off so being illegal the smallest little bit will help the shooter. If the player screened is contacted illegally and slowed one step it will make all the difference in the world for a shooter or a player that cuts to the basket once the defensive player arrives late as a result of the illegal screen. Look for players taking the contact to the person they wish to screen and look for elbows and knees coming out for ineffective screens.
In time it will come much easier. I think one thing the original poster pointed out alluded to watching the ball. This could be a bigger problem than calling illegal screens.