I used three sewing feet to achieve this pocket - an invisible foot, a zipper foot and a normal sewing foot.
With pins, I marked where the zipper would start and finish on both pieces. I made sure the zipper wouldn't interfere with buttonholes, centre front lines or seam allowances.
I pinned the zipper in place and made sure the zipper closed at the front, so you can see the zipper pull. The choice of how you want to open/close the zipper is yours.
Here's where the invisible zipper foot helps sew the zipper on, stitching under the zipper coils.
Then it was time to match the other side of the zipper and darts.Then I closed the top and bottom front pieces using a zipper foot. I sewed from the zipper to the edges to ensure the seam sewing matched - no puckers.
Here's the pocket bag, sewn onto the zipper seam allowances and then the side seams are sewn closed. Again, my measurement of the pocket bag was just deep enough for a card and some money to buy coffee in the morning. It's more aesthetic than functional.
And here's how it looks on the front. Phew!
Don't just look at what I've done, go to some real references.
Singer Tailoring - 1988,
Jackets for real people by Alto, Neall and Palmer - 2006,
New Simplicity Sewing Book - 1979