First sharpen the front of the blade, so it's flat and at the right angle.
Then when the front of the blade is flat, sharpen each side of the front of the blade so it has an edge.
Don't make the edge too sharp or it'll wear faster.
You may have to file away the first tooth if there's significant wear to the front of the pick. This is because you want the bottom front of the pick to penetrate the ice before the teeth.
If you have to file away more than the first tooth to make sure the front of the pick penetrates first, it's time to buy new picks.
The bottom, front corner of the pick needs to be sharp but the bottom, top corner of the pick can be rounded.
I think this is what the Andy Turner article says, and I applied it. There is also useful a very good, detailed section on this in this book
http://www.amazon.co.uk/Winter-Climbing-Rockfax-Guide/dp/1873341962/ref=sr_...