Great site with very clear directions and many yarn choices http://www.doctorwhoscarf.com/
Another site with different yarn choices and slightly different instructions. http://wittylittleknitter.com/ The Vanna's Choice yarn is available at Jo-Ann.
For dolls use as light of a weight yarn as possible and small needles, look on the label for a square the smaller the number the smaller the needles etc. Keep all our yarns the same number. Larger minis and bigger can do sport weight 3-4, smaller dolls need a microspun or crochet thread if you can find the colors, if not just work on as small of a set of needles as you can stand. I found success by only doing half the number of rows in the patterns given by the first site, make it just wider than the doll's neck is long.