All good advice above.
1) Always know where the ball is (sometimes you will have to look away to glance for runners touching, possible OBS). Just know where the ball is at all times and where it could potentially go. Trust typical baseball instincts.
2) TIMING TIMING TIMING. Don't get jumpy. See the play, see it again in your head, call it. This goes for balls / strikes, safe/outs, fair/foul. Nobody is going to give you grief if you wait a beat to make a call. Take your time, it will save you a lot of trouble throughout your umpiring career.
3) Be confident. On your ball field, there are two rules that you must agree with in your own psyche. a) You're always right b) If you're wrong, see rule a. After the game, you can admit fault in your own head. But don't do it during the game. Convince yourself every call was the right one. Display that confidence to game participants if questioned.
10 games in, come back and post how you've been doing. 10 games in will be a good time to set up some goals for the season that can be re-evaulated in October or November. Without goals, we don't know where we should be going
I'd say these 3 tips should give you an enjoyable start. Umpiring doesn't look difficult or sound difficult, but it is. The pursuit of perfection is most enjoyable, but probably not attainable. Which is what makes umpiring one of my passions. I hope it becomes one for you too, and you continue to want to learn about umpiring.
Cheers mate!