There is no rule saying you have to aim at the second arrow. If you’re throwing a huge hook, maybe you want to aim at the first arrow. If you’re having trouble throwing a hook, you might want to aim more toward the middle.
Another simple adjustment is speed. A good way to get more hook on the ball is to throw it slower.
However, when first trying to find your strike ball, the simplest adjustment is the starting position. You’ll find yourself naturally making the other adjustments as you get more practice and get a better feel for throwing your ball.