There are a number of tutorials on the web - I followed this one and this one. Naturally I had to complicate things by only sewing one side seam. Accordingly I had to cut then bind the other armhole (otherwise you'd just end the seam below your armpit, as you do on the seamed side).
Ever since Meggipeg mentioned it in her blog, I've been paranoid about pattern placement , so I knew I had to offset the pattern so as not to inadvertently lead the eye when you don't want it led (ie don't place a blossom smack bang over a breast - unless that's your thing, of course!). I hope I got it right:
And I found a hat to match!