Whenever I am first teaching someone to knit the hardest concept to impart is twisted stitches. For some it is natural to wrap the yarn clockwise around the needle and create a stitch that is twisted. While this is by no means ‘wrong’ it is important to know the difference between a twisted stitch and a regular stitch. The second part to knowing the difference between the two, is knowing how to fix a twisted stitch.
Here are a few videos about how to fix twisted or backwards stitches.
Unfortunately there is not too much to say about this kind of technique because it is something you need to see in order to recognize. Note that when used correctly they can add body and texture to knitting, so don’t think they are always a mistake. I have seen patterns, mostly with cables, that add in twisted stitches for a little extra umph. For newer knitters though, this can be a pitfall you wish to avoid. I strongly suggest getting to know what a twisted stitch looks like, eventually you will be able to feel it in your knitting as you go along.
I usually get them when I have picked up a whole bunch of stitches because I had to frog something down. Rest assured that this is something everyone goes through. The way I learned about twisted stitches was from frogging a bottom-up sweater from the shoulders down to the armpits, I picked up the stitches again but they looked wrong. At this point in my knitting career I didn’t know what was wrong or how to fix it, so I ended up frogging the whole thing. Later I realized that all the stitches were twisted, At the time I had just assumed that I split the yarn when I was picking up the stitches. Learn from my mistakes and avoid needless frogging!