Those are called ladders.
If you are knitting something that will not be reversed or flipped up like a hat brim or sleeve cuff AND you are knitting in the round you can try my method. I had a hard time with this very problem so I figured out a way to do it so that the outside looks perfect. The inside has twisted stitches which is why you can't flip the edge.
Also try holding the needles together more at the joins...the one you just crossed and the one you are coming to. It feels awkward, but it really does help.
Practice is the best way to improve it so keep at it!