In addition to DannyHoops posted, here’s a helpful set of pictures about batters and there arm placement.
I should note that not ever batter will react and pose himself in a predictable way across the board, So, learn by selecting one kind of posture or pose and work it. Just remember your batting order logic - 1,2,3 and sometimes 4th batter are in the top of the order for a reason. These guys are good with the bat and should warrant your best stuff that matches your memory of what works best against what batter type. 4,5,and 6 are usually less capable, but can hold their own. And the 7,8 and 9 are usually at the bottom of the order for a reason - but don’t take these guys for granted and get fancy. Go right after them with strikes.
Where and how a batter holds the bat can indicate a high percentage of the time where he’ll place the ball in the field.