Step 1: Pin & Sew the Crotch Seam
Step 2: Press Back Half Right Side Seam Allowance.
Step 3: Pin & Tack Zip on Right Side.
(While you're at this side, it could be a good time to prepare the zip shield & sew it all up together now rather than later)
Step 4: Prepare the Left Fly Facing...
Zig zag the curved edge.
Step 5: Sew on the Left Fly Facing
Step 6: Pin Left Fly Facing Back
Press & top stitch.
Step 7: Prepare the Zip Shield
Step 8: Pin, Tack & Sew Right Side
Through all layers, locking the zip between the right fly front & zip shield.
Sew close to the zip at the front.
(In this picture I have already tacked the left side of my zip to the left fly facing)
Step 9: Pin Left Side of Zip to Left Fly Facing...
Check it looks ok from the front & tack left side of zip to left fly facing only.
Pin the zip shield out of the way & sew the left side.
Step 10: Top Stitch the Fly
In a curve from the bottom of the fly opening, up in a straight line to the top of the waist seam.