There are as many different spare-shooting methods as there are types of bowlers. You should try a few to find the one that gives you the most room for error, and makes you feel comfortable lining up for spares.
The one I've been practicing lately is to use the same arrow for all your spares, and move your feet around to achieve the desired results. As presented by Susie Minshew in "Focused for Bowling", by Dean Hinitz, you use the 4th arrow as your target. However, I've settled on the 3rd arrow for the 4-7, the 2 and the 3 pin, while using 18 for the 6-10. I stand on 16, 19, 22 and 35, respectively.
This is because I am extremely right-eye dominant, and when I line up for left-side spares using the 4th arrow, I feel like I'm going to throw the ball straight into the left ditch, so I'm more comfortable looking at the 3rd arrow, which appears to me to be in the center of the lane.
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seadrive
Cogito ergo bowl