Mark your placement markings on the main fabric for where the pocket needs to eventually be sewn.
Cut two pockets pieces. The pocket lining should be cut smaller than the main piece. Fold the main piece (or pattern piece) at the top, over enough to account for both 1/2 inch seam allowance plus the upper stitch line. Cut the facing that size of the folded main piece
Pin the top edge of the lining to the top edge of the pocket (no longer folded), correct sides together
Sew 1/4 inch from top, leaving a gap in the middle for tuning.
(you can see I forgot to leave the opening and had to pick out some stitches. I’m super awesome like that.)
Press seam allowance open
Fold the long facing/main fabric pocket piece correct sides together, all raw edges matching. The seam allowance with the gap will be a little down from the top. Pin in place
See, here is your little gap
Sew from one top corner, backstitch, down the side, across the bottom, up the other side to the other top corner and finish with a backstitch
Clip corners and seam allowance excess
Turn pocket piece right side out through the little gap you left before
Handsew the gap closed on the inside, making sure to not catch the front facing fabric as you go
Pin pocket in place
Sew pocket in place, backstitching at corners