I would bare shaft test. Stand about 4 or 5 yards from a target, shoot shafts with light arrowheads. If tail goes left (assuming you're an average archer, left side of bow), I would guess that the spine is weak, and you need to draw less or reduce the weight of the arrowhead. If stiff, draw more or increase arrowhead weight. Once they fly pretty straight, then I'd fletch.. but that's just me. Maybe I'd try different distances as well before fletching like 10 and 20 yards and see how they fly.
Besides that, a spine tester should be useful. If you're way off then adjusting arrowhead weight probably won't help much.
Something.
What sucks is I'd like arrows that can be nocked either way with the Y style fletchings so I can nock without looking and maybe shoot pretty fast one day.. maybe I'll just find a side such that the stiffness is the same both ways