Prepare your fused button stand (or front plackets as they are commonly called) by pressing them vertically in half (wrong sides together) to create a sharp fold line down the centre.
Open out the folded placket and place onto the front edge of the shirt (right sides together) and pin in place.
Stitch a 1cm seam from neck to hem.
It's tempting to sew this straight, long seam fast without much attention, but it's very important that this seam is straight and accurate and your seam allowance does not waver over 1cm, otherwise you will find it hard to get a nice finish at the last step.
Press the seam allowance towards the inside of the placket and away from the shirt.
Press a 1cm seam allowance under, on the opposite side of the placket. You need to check that when the placket folds in half it covers the first row of stitching. I've found the easiest way to do this, is to actually fold the placket in half first and then tuck the seam allowance under bit by bit and press it into place with the iron.
This is what the folded placket should look like - notice the stitch line is hidden under the fold line.
Pin the placket down in place, from the top side.
The final step is to edgestitch the placket down - you want to check as you sew that the underneath layer is being caught at the same time - the best way to do this is to feel the underneath layer with your fingers as you sew, to feel if it's in the right place.
ALTERNATIVE PLACKET METHOD
There is an alternative way to topstitch your placket inplace. The method above, is a common way for women's shirts and blouses - however depending on the style of your shirt (for instance, if you want a different a width of topstitch to match other areas on your shirt) you can follow steps 1-7 exactly the same, and then follow on from these steps below instead.
Instead of edge stitching your placket down, you ditch stitch the placket in place. "Ditch stitching" is basically what it sounds like, stitching in the hollow (or ditch) of a seam that has already been sewn. You will notice that needle in the photo above is EXACTLY in the seam line. it is not catching the top layer of the placket down.
It is slightly more fiddly than edgestitching but gives an invisible finish on the top.
This is what the ditch stitched placket looks like, the stitching is completely invisible from the top (and just an edgestitch on the inside). If you want a clean finish you can leave it like this.
With a ditch stitched placket application, you are free to do any kind of decorative topstitch. I've chosen to do a 5mm topstitch either side of the placket to match the topstitching on my yoke.
Repeat the same steps for your placket on both sides.