I like to start out around 7-1/2" (throat to the string)by shooting different shafts, and bare shafts. A shaft without feathers, that is too stiff will hit nock left (RT Handed), and nock will be right if it is too weak; even when the feathered arrow seems to fly okay. If I can't get it to fly straight and group, I start raising the string by twisting. Flemish stings are best for this test. However, when you find what works, you may need a different string if you have it twisted too tight. I prefer 2 twist per inch.
You can also add point weight if the shaft is too stiff, or lighter if too weak.