Received wisdom is that to get sharp corners you need to trim them at 45 degrees.
Well, I’ve been making rather a lot of waistbands recently and have found this method gives me much pointier corners than trimming and, if you think about it, actually reinforces the corner too.
If you’ve got 2 seams joining at said corner (here one of the sides of my corner is a folded edge), fold the seam allowances on top of each other so that they overlap.
If you’re using a very bulky fabric you’d probably want to layer the seam allowances first (trim one layer of the seam allowance shorter than the other).
Wendy Ward 