I has to do with how you insert the needle into the stitch you're tinking. I think in this video you can see how it should be done. http://www.youtube.com/watch?v=OkXdqQnU7Pw
I thought there was a video on this site but I can't find it.
ETA This shows how to knit into a stitch that's turned the wrong way and avoid twisted stitches. http://www.knittinghelp.com/video/pl...isted-stitches