Sew the pant legs closed along the inseam.
Serge the seam allowances and press them toward the back of the trousers.
Repeat for the other side.
Sew the left fly to the left front of the trousers along the centermost edges, right sides together, and leaving the bottom ⅝” of the fly hanging free.
Sew the two pant legs together along the center back and lower front – all the way from the upper back, to exactly where the left fly stitching ended – matching inseams and pinstripes. Reinforce the stitching beneath the left fly.
Press the seam allowances open.
Turn the left fly under and press.
Pull the left side of the trousers out of the way.
Using your zipper/piping foot, sew the zipper to the trousers, stitching close to the zipper teeth.
Then, using your all-purpose sewing foot, stitch again through both layers.
Using your quilting/walking foot, topstitch the left fly into place through all layers.
(You can use the guideline on the printed pattern, but I prefer to simply stitch from the underside, using the edge of the left fly as a guide.)
On one of your right flies (piece EE), serge the outer/vertical edge.
On the other, bind the outer edge with the same bias tape you used on the left fly and center back seam allowances.
Position this right fly piece underneath the right side of the zipper so the upper edges and seam lines are flush.
Note that the right fly will actually extend about ¼” past the zipper tape.
From the underside of the right zipper/fly, using your zipper/piping foot, sew the right fly to the trousers close to the previous (zipper) stitch line.
As with the left fly, leave the bottom ⅝” hanging free.
Trim the top of the zipper so the upper edges are flush, if you’d like – but if you trim past the zipper stop, remember not to zip your zipper up past where it should be! You don’t want to accidentally pull off the zipper pull tab!