I set the twist in my yarn before I knit or if I find that my spinning has been very un-even (like when I've done my spinning in multiple settings in a variety of locations over a period of weeks - rather than in one steady marathon Saturday afternoon...). I skein my yarn and dampen it, then hang it over a hanger with a weight on the bottom (mostly full windex bottle) to dry.

I've found that setting the twist isn't as necessary before weaving as it is before knitting.

If I were to ply my yarn before weaving it, it would be twice the diameter that it is as a single... there would therefore be fewer picks (passes of the weft yarn) per inch and that would make the weaving go faster.