Make a general shape around it - leave a border of junk. After you isolate the part you want, you can select the junk with the magic wand individually and delete.
that's how I finally got doMima's head and hair.
Unless there's a very clear distinction between the interesting part and the background, you have to do it this way.
Also, coollew said to zoom way in and use the eraser tool around the edges. At the top you'll see a width thingy for the eraser. This will help a LOT.