These are probably the three best ways to read a hitter.
1) Where a hitter stands in the batter's box
a) If a hitter is up in batter's box (meaning he is closest to the pitcher), this usually means that he has trouble hitting the breaking balls or really any off speed pitches like curve ball, change up, slider, or split finger.
b) On the other hand if a batter stands back in the batter's box (toward the catcher), this means he has trouble with fastballs. He stands in the back of the box so he can have time to catch up to the baseball and see it longer.
c) If a hitter stands on top of the plate (close to the plate), it means he has trouble with the outside pitch.
d) If a hitter stands away from the plate, it means he has trouble with the inside pitch. Now this doesn't automatically tell us where to throw the baseball. Here's why. If a hitter is up in the batter's box it means he has trouble with hitting the breaking balls. The problem is that he has adjusted to try to help himself hit those breaking balls. A good pitch to throw would actually be a fastball. You first have to make a batter honest and then dominate his weaknesses. If you threw a fastball to this guy first pitch, he would have to get away from protecting himself from the breaking balls or he is going to get beaten by fastballs. That's the best thing about reading a hitter is that once you see something, you have the advantage and you can dominate a hitter.
2) Reading a hitter's hands
a) If you notice that a batter has slow hands then you know that he has trouble with fastballs. Once you notice a hitter has slow hands you should stick with locating your fastball in different spots. Once you decide to go to an off speed pitch all you have done is speed his bat up. You are throwing a pitch that works well with the speed of his hands. This is never a good idea even if you have a guy 0-2. If he has slow hands, throw him a fastball.
b) On the other hand, if you notice a batter has quick hands then you know that he can hit the fast ball. The only problem here is that because he has quick hands, he may be able to adjust and hit the off speed too. These guys are a little bit trickier to pitch to. My suggestion would be to keep him honest and throw him some fastballs. Even though he can hit the fastball, throwing them will make you breaking stuff that much better against this type of hitter. Once he has seen a fastball, you are hoping that he will be out in front of your breaking stuff.
3) How a hitter stands (open or closed)
a) An open stance usually means that a hitter has trouble seeing pitches. He may open his stance for comfort or to see the baseball better. Whatever the reason he is leaving his hips open. As a pitcher when you see this you should throw inside fastballs. The hitter is already sacraficing some power by opening his stance. By going inside we are forcing him to stay open and take that loss of power. These guys are easy to jam up and get a lot of pop outs on.
b) A closed stance usually means that this batter has a problem stepping in the bucket. He closes his stance to correct this. These guys usually have trouble hitting the outside pitch. Even though their stance gives them the best opportunity to hit the outside pitch I think a low and away fastball would work on this guys. They are standing that way for a reason. Let's see if they can hit it and then try a different approach.