These are the pieces you need for this pocket: an under pocket lining, two 1.5 inch welts, 2 inch facing, and a top pocket lining that is .5 inch longer than the under pocket lining.
Mark your pocket placement on the main fabric
Fold both welt pieces in half and press
Place on right side of garment, right sides up, on either side of the pocket placement, raw edges on the marking. Baste in place
Sew your facing to the under pocket lining, right sides together along the top
Place the under pocket lining, with facing, over the top welt, right sides together.
Place the top pocket piece over the bottom welt, right sides together
Sew a cute little rectangle 1/4 inch around where the pocket opening needs to be, through all layers of fabric
Cut open through the main piece
Pull the pocket through to the back
Sew the pocket pieces together