Why systems beat guessing
Spare shooting is a geometry problem with a repeatable answer. Instead of eyeballing each leave, a spare system gives you a fixed starting position and target for any given pin or cluster. You execute the same kinds of shots over and over, which is exactly what builds reliability under pressure.
The 3-6-9 system
The 3-6-9 system is the most popular for hook bowlers. You pick a baseline shot at your strike target, then move your feet a set number of boards (3, 6, or 9) depending on which pins you're shooting, keeping your target over the arrows the same. The numbers come from how board moves translate to pin coverage. It's especially handy because it lets a bowler who hooks the ball still shoot spares accurately without throwing perfectly straight.
Straighter is safer for spares
For single corner pins, many bowlers reduce their hook — squaring up and throwing straighter — because a hooking ball has more ways to miss a lone pin. This is the main reason serious bowlers keep a plastic spare ball: plastic barely hooks, so it goes where you aim, making corner pins far more makeable. A dedicated plastic ball is one of the cheapest, highest-value additions to a bag.
Shooting the corners
The 10 pin (right corner for a righty) and 7 pin (left corner) are the classic single-pin tests. The cross-lane angle — standing on the opposite side and throwing across to the corner — is the standard approach, and a near-straight ball makes it repeatable. Drilling these two shots until they're automatic pays off every single game.
Splits
Splits — two or more pins with a gap where pins were cleared — range from makeable (the 'baby split,' 2-7 or 3-10) to nearly impossible (the dreaded 7-10). For makeable splits, the usual strategy is to clip one pin thin enough to slide it into the other. Some splits are simply about minimizing damage by guaranteeing one pin. Knowing which is which keeps you from throwing away a frame chasing a miracle.