1) I used a contrasting thread on Marigold's buttons holes, so I sure didn't want crooked threaded openings! Yes, modern machines are programmable to sew buttonholes neatly and repetively, but I'm often challenged by accurate placement. So I draw my buttonholes on medical supply tissue paper and sew them one at a time.
I make test sewing samples first
Fabric Test Package - I make sure to include a piece of the same interfacing between two pieces of the shirt's fabric, so that I'm testing the same situation as my shirt
2) First I laid the buttons down on tissue. In theory you add maybe 1/8" over the width of the button. I try by theory and I try my gut reaction. Then I sew, cut and try the button in each hole
3) I make sure to put a wide pencil line at top and bottom - this is where a programmed buttonhole knows how far to go - but I making the decision in each case to stop or turn.
That's because of experience. Sometimes the fabric or interfacing gets stuck in the machine (even though I always use the right presser foot), and the programmed stitches aren't even on both sides. I use my buttonhole machine setting, but I make the choices each time as though I'm sewing the first, and I no longer use the programmed setting.
4) When I cut the button hole, of course I put a pin across the top so the seam ripper I'm using to open the buttonhole, doesn't slice past the top of the opening. Again... experience!
5) When test sewing these buttonholes, I found I needed a piece of tissue underneath, as well as on top, in order to make the interfaced fabric test package (in preparation for the actual shirt) move unstickily along. I don't usually need the underneath tissue, but this fabric is a kind of loose, rough weave, and I found this quite helpful to keep my machine sewing smoothly.
~ ~ ~Marigold - A Princess-Seamed Shirt - Terminado - http://meencantacoser.blogspot.com/2016/11/fall-colors-marigold-princess-seamed.html