Here is a tutorial on adding flat pockets to the front of pants.
Here is one on adding pockets to the waistband of regular elastic pants.
Here is one for adding pockets to one piece pants.
This photo is of my first attempt at following one of these tutorials. I followed the first one and think it went just OK. I think they are slightly lopsided from one leg to the other, which is unfortunate since these are in wool suiting, and meant to be dress-up pants. I haven't ironed them yet, but think that won't help their unfortunate placement.
Stay tuned for further pocket additions.