Because of my different backgrounds in sewing, I have picked up a couple of tips to make clothes look professionally made. This tip works for all kinds of faced collars, faced pocket flaps, faced pockets, etc. (This is not for facing necklines and sleeves though!)
Pin your collar and it’s facing right sides together. The key is to pull the facing 1/8″ past the edge of the collar on all edges except the neck edge. In this picture I have pulled the navy fabric, the facing, out on all edges except the bottom neckline edge. Sew them together with the regular seam allowances. This means, if you are sewing at 1/2″ you will sew 1/2″ from the collar edge, not the facing edge!
Trim and grade the seam allowances, and turn the collar right side out. Without any ironing, the collar will curl towards the facing!
When you sew the collar on, it will curl down towards the body like a collar should.