Background blur is called "BOKEH" which is a Japanese term for the subjective aesthetic quality of out-of-focus areas of a photographic image.
Focus on the eyes...if they are in focus..the whole face will appear to be in focus. And it is a combination of f-stop and focal length, shutter speed, etc..
Here is a good explanation on how to increase background blur.
http://www.dofmaster.com/backgroundblur.html
And then I use this when I'm "planning" a shot well ahead of time.. i want a palm or something to load a portable version on.
http://www.dofmaster.com/dofjs.html