I've done a special post for the Sewaholic Robson Trench Sew Along on attaching the pockets. This is a traditional trench coat pocket with a flap and inseam pockets. The primary trick in getting the pockets to look perfect is precise marking. There are notches and seam allowances that should be marked. You can see both marked in white below.
HERE. Hopefully between the written pattern instructions and my instructions you'll be able to sail through the process of attaching your pockets.