Start with Auto Mode
MLB 9 Innings Baseball 20 starts you with an automated mode when playing games. This means that you don't need to worry about things like running on the basepaths or making defensive plays. They start you out with it, and I'd recommend leaving it on if you don't feel comfortable.
The only things you do need to do is throw pitches, hit, and make throws defensively. Throwing on defense is pretty easy. Just slide your finger in the direction of the base you want to get the ball to. Heck and don't forget, you can choose to only hit or pitch if you don't want to do both right away.
But, once you feel ready, try turning off the automotive setting and see how you like it. If you find it too difficult, then feel free to fire it back on. Maybe you never want to use manual mode, and that's totally fine as well. However you do it, it'll be fun.
Mix up pitches on the mound
This basically is the same thing to remember when playing any baseball game but of course, AI opponents vary in different games. But mixing up your pitches is a great way to dominate on the mound. If you have a good starter who has a nice balance of pitches, use them all.
You can mix it up any way you want, but if you can, try switching between fast and slow pitches. Starting with a fastball in the top or bottom corners might be a good way to start. This is because the majority of the time, the hitter will take the pitch. Just put it in a good spot, because fastballs can get hammered if you're not careful.
But after getting them to take (or swing at) the fastball, hit them with something slower like a changeup or curveball. Sometimes you'll get a batter swinging out of shoes and there's nothing more satisfying than that. Now, when you bring in relievers, you'll notice that their number of pitches could be limited. Do the same thing though; mix up the pitches that they offer.
Hitting is all about timing
With a tap of a button on the right side of your screen, you'll able to smack balls all over the field. Alas, it's not that simple, as you need to make sure to Time the pitches right. It's everything when at the dish, and it feels great once you get a base knock or better.
This is more of a general rule of thumb but, try not to swing at every pitch. It's so easy to lick your chops and get ready to swing and crush the ball. Well, unfortunately, that's not always going to be the case, so be smart at the plate which I'm sure you will.
Keep an eye out for pitch speeds too. As mentioned, fastballs will go significantly quicker as opposed to a changeup so keep this in mind. Try to hit any pitch that's in the zone, but if the ball is higher, then you may have a better chance for a home run, especially with a powerful hitter at the plate.
Check out your pitcher's energy
It's really easy to overlook the energy meter of your starting pitcher. Take a look at it from time to time to see where he's at. This is important because his performance will dampen if it gets to low. The poor guy will be too tired to throw pitches effectively.
And by not throwing pitches well, there's a chance you'll get whacked by the opponent. I made myself look dumb (although I'm dumb anyway) by leaving my starter in there one time without checking his energy. As you might've expected, I got taken deep by the other team.
So make sure to put in a reliever to take over for your starter. The nice thing is that you don't need to get them warmed up before putting them in. Grab your next best one and let it rip. Then, when you get to the 8th or 9th inning, make sure to put in your closing pitcher (if you're leading). On most teams, closers are the best pitchers in the bullpen so if that's the case with your favorite team, then use him, and slam the door shut.