Mantis
The answer to your question depends on what kind of spare you are converting. If, for example, you had a single-pin leave, say, 5 pin or 1 pin, you would play your normal strike line, perhaps moving a board towards the side of your bowling hand to maximise impact, but accuracy is paramount here. For other spares, it's more a trial and error thing where pins left standing right of centre you would normally move left and vice versa. If you have left several pins, you need to make sure you aim your shot so that the first pin your ball has contact with is the one nearest to you. This pin is the referred to by some as the KEY PIN. Once you have identified your key pin you can position yourself so that when you play the shot, it's the first pin you hit. For example, if you've left a 2-5 spare, aim for the 2 pin, if you've left a 3-6 spare, aim for the 3 pin.
I hope thats some kind of use to you
Laters
Space Cowboy