This technique is a bit of a mish mash of techniques from various sewists including Debbie Cook.
Step 1. Make the collar.
Step 2. Baste the collar stand.
With RS together, baste the neck edge of the collar stands together using a long basting stitch. Press this seam open, hard, then remove the stitches. This step keeps both collar stand seam allowances even and sets them up for the final line of stitching.
Step 3. Stitch the collar to the stand.
Sandwich the collar in between the collar stands with wrong end of the collar against right side of the outer collar stand, lining up pattern markings and paying attention to the markings on the top of the collar band and where the collar ends. Stitch the collar to the collar stand, around the curved corner and right across your pressed-up seam allowances on the curved ends. Start stitching at the CB so you can stitch each curved end nicely.
Trim this seam closely but leave the seam allowances a little longer at the neck edge so there are no frayed seam allowances near the curved edge of the collar. Don't snip the corner point off the collar stands. Notch the curve of the seam allowance near the points. Remove collar basting. Turn collar to right side and press.
Step 4. Prepare the neckline
Stay stitch the neck edge of the shirt and clip it often to allow the seam line to lie straight.
Step 5. Sew the collar/collar stand to the neckline
Pin the outer collar/collar stand to the neck edge, leaving the inner pressed edge free, and make sure it fits exactly with the collar stand point nice and tight in against the neck edge. If the neckline is a shade too long, take in the shoulder seams a bit.
Sew the outer collar stand to the neck edge, leaving the first and last 5/8" or so of the seam unsewn, and stitching along the pressed line. If the seam allowances are big, trim them. You could also trim the seam allowance of the pressed under inner band now too.
Step 6. Topstitch
Flip the pressed edge of the inner collar stand down and baste in place. Top-stitch all around the band, starting at the CB and using a 'jumper' at the collar stand points.