http://www.youtube.com/watch?v=xls25e08sSg

Really nothing is more helpful then this. You can do the same in xsi

I prefer the method of starting with a plane on the nose, mouth and eye then extruding out, as long as you plan out your loops well you get a good result with a lot of control and little tweaking in the end is needed.

It's mostly preference though, this was my most recent.