Focus on throwing one pitch at a time. Don't worry about the last pitch.
A lot of young pitcher's will throw high, then over compensate with a very low throw - sometimes in the dirt. With the pitcher behind in the count, the next pitch might be down the middle of the plate for a single.
The pitcher should forget about the previous pitch and focus on throwing strikes low and away (over the outside of the plate). Take a deep breath, smile and then go after the batter.
If there are two outs, then focus on the catcher's glove and don't worry about runners on base. Throwing over to keep a runner on first base can mess with your rhythm, so check the runner then throw hard to the glove. A ground ball should result in an out at first base.