Start at full length which should give you a weak arrow (nock left for right hander), cut in small increments until you have an arrow tuned to your bow. After all you can’t add back what has been cut. This is how I was shown to bare shaft tune.

What Fishon says pretty much nails it. And doubly so if you want to experiment with different point weights/FOC. In my limited experience with carbons, I find them to have far wider spine ranges than woods.