I am a big fan of facings - if they are well designed and correctly sewn they give a stable professional finish. I'm not a fan of lining right to the edge of a garment because a) it is noticeable, and b) it doesn't wear very well. Normally I would use self-fabric facings, but here I am using some black lightweight wool because I didn't have enough tweed for the facings!
Now check your armholes - if you have estimated cloth allowance correctly, the raw edges of your facing should lie 2-4mm short of the shell as it does below. If you haven't got it right, you can trim it slightly (unless you are working in production, when you inform the patternmaker!).
To bag out the armhole, start at the shoulder:
Start sewing at the shoulder seam:
and sew down to the side seam, and up the other side, matching any notches and manouvering the fabric as you go. It is important to align all notches and seams so that no twisting occurs, and try not to stretch the fabric around the curves or you could mishape the armhole.
Sew right to your start point at the shoulder seam:
Clip, turn, then understitch the facing (to understitch, stitch through facing and seam allowance, 1mm from seam - shown below). Begin at, or as close as you can to the shoulder seam, stitching down towards the side seam and up again to the shoulder seam as far as you can neatly go:
If your shoulder strap is wide you will be able to understitch right around the armhole, for this style I could only stitch to within 3cm of the shoulder seam:
Press, and admire your work!
I hope this helps in your sewing! As usual, I am happy to answer any questions in the comments.
And in case you are wondering, the boucle check fabric is soon going to be a Chanel jacket!