Below is a suggestion I made for a similar problem over in the "Ask the Instructor" forum. In your case, make the shot straight. (Your problem likely stems from your head being in the wrong position so you don't see the shot accurately, but it could be due to other issues.)
As for which ball you should be looking at last, I recommend the object ball especially for beginnerrs. I think you need the immediate feedback when you hit it wrong. If you are looking at the cue ball during your forward stroke, either that feedback is delayed or your eyes will be suddenly shifting at the instant of contact.
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... First mark the center of the pocket with a white donut (paper reinforcement). For this purpose the "center of the pocket" is described in this article:
http://www.sfbilliards.com/articles/1997-04.pdf
Put a coin on the table about two diamonds from the pocket. (The angle from the pocket -- straight out, along the cushion, something in between -- is up to you.) Put the cue ball by the coin. Put an object ball half way between the cue ball and the pocket. You can put it so it's straight in or with a small angle.
Shoot the shot. Make sure you send the object ball over the white donut. Sliding into the side of the pocket is not good enough -- you need to be pretty much over the donut. When you do three good shots in a row, move the coin six inches back and start a new series.
Notice which side you favor. Use cuts to both the left and right. If there is a "bad side" spend more time on it.
When you get to a distance that you can't do three in a row even in 15 shots, take the coin back to the start and vary something. You can vary the angle, speed, spin, etc. Stay relatively consistent within each run.
Always, always, always strive to drive the object ball directly over the donut.
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