If you're shooting a single bevel broadhead, it's a good idea to match fletching direction with bevel direction so both components work to spin the arrow in the same direction.
If you're not shooting a single bevel, it doesn't matter which way you fletch. Some folks will advise you to "clock" your arrows and fletch to complement natural/bareshaft rotation direction. Clocking is a waste of time IMO, but if it makes you feel better, waste away. The arrow will be spinning in the direction of the fletching within a few feet of launch whether you fletch with or against natural rotation direction.
Regarding amount of offset/helical: the greater the angle, the more drag the fletching will induce, and the better able it will be to steer/stabilize the arrow. Like other aspects of fletching (e.g., vane count, height, length), it's difficult to say a priori how much offset/helical angle is enough. If you like to tinker, fletch up a few different configurations and see which groups best with broadheads. If you want to just do it once, three high profile vanes (e.g., Bohning Blazer, AAE Max Hunter) at 2-3° offset is a popular choice that works well with most broadheads.
