I usually just keep the strands across the back loosely. There really isn't any need to twist them--I think you're making a lot of extra work for yourself. If you keep the yarns in the same place as you go--one on 'top' of the other--then you should never have to untangle your yarns. When I say 'on top,' I mean like this--
I don't know that there'd be any drawback in the end product, but I also don't see any advantage. If you have a long strand in back, then you should catch it to keep it from being too long, but otherwise it's not necessary to do anything special.
"Trust the pattern!"
Time flies like an arrow, but fruit flies like a banana.
Hop aboard while we follow the cloud-covered van of knitting harmony, man!! Woooo!! --Hedgehog
IngridKH on Ravelry