I need pockets, and generally the clothes that I like at second-hand shops don't have any (or enough, or they're fake, or...). So I poked around Instructables hoping for some guidance, and didn't find much. Here's what I did, largely based on this tutorial I found.
[EDIT : I later found this Instructable, which is has excellent action shots! ^_^ ]
To make the pocket shape, I traced around my hand on a piece of card because I don't have any similar garments with pockets to trace instead. (If you do, it'll work like a dream!)
I recommend marking where you want the pocket to be at this point. Put a pin through the seam at the top and bottom of the pocket so that you know where to open them.