Stroke Builder Drills
The drills are primarily about improving your stroke itself. The aim is to get you stroking perfectly straight through the ball, and able to hit the ball on the exact vertical centerline every time. Until you can do this repeatably, you will be missing balls and not know if the fault was a crooked stroke or a hit on the cue ball that was not in the intended location.
You should do these drills regularly until you can make 10 in a row easily. Then you should come back to them any time you start to have difficulty, to make sure that your stroke is true.