Sight down a bare shaft, and mark the high spot and put a pencil mark at one end as a reference. For shafts with difficult bends, use a tool for aligning broadheads, you can see the shaft wobble, again find the high side, and mark. Then use a large screw driver to rub the high spots. Put one end on a table, hold the other with the pencil mark up, and rub back and forth over the high spot. If needed apply more, and more pressure. The shaft will hold and stay straight longer. I usually spine the shaft to check for straightness before putting on a finish.
If you use tapered shafts, and you bundle them, don't put the rubber band over the tapered end.