Baste collar on using 1/8" seam allowance. Follow bias finish to have bias inside the garment instructions in your pattern. Then when you go to sew the other side down, flip the collar up and stitch along the outer edges, under the collar area.
Clip your curves before sewing down the inner edge. And take out the bulk at the side/shoulder seam to reduce bulk.
And thats about it! I gave the collar a good press and it stayed down. If you want, you can fold the collar down and edge stitch it in place.I found after I washed and dried it, the collar needed a good press and then was fine.
Ok now the flat ribbon tutorial. Make your sash per instructions in the Angie pattern. Then make a second one half the total length. Finish all edges. Then you are going to lay it out and figure your lengths desired.