for doll hair, you can wrap the yarn back and forth along a ruler or something like that and then cut the loops, to make the hair even. then i lie the hair over a strip of paper and sew at the part. I usually do two like this- one i sew onto the top of the head and the other perpendicular up the back. then i trim the bangs and put the other side over the back and split the back section at the part to tie into pigtails.
i use a large needle to sew the "wig pieces" onto the head.