How to get sharp corners

[spottygymbag]

I'm newish to sewing (dabbled over the years and can follow a pattern, sew basic pieces etc) but the one thing that has always eluded me is how to get perfect sharp corners. I'm making some fabric book covers and I'm really trying to achieve a nice sharp, flat corner but they keep coming out rounded and thick. I'm using thin cotton or cotton blend fabric with no stretch with the patterned fabric on the outside and a liner on the inside leaf of the book (not sure if that makes sense?).
What are your tips and tricks for this? What am I doing wrong?

I'm not very good at sewing, but are you cutting the seam allowance at a 45 degree angle so you haven't got loads of it bunched up inside the corner?

Yes, definitely cutting the angle. I've experimented with how close I can cut it and not have anything escape with varying results 😂. I do also iron everything so it's beautifully flat and aligned. I'm a perfectionist so not being able to get these corners right is really doing my head in!

Can't really explain it well - but I'd try doing it in two stages, 1st stitch the two 'side' edges press them open, 2nd stitch across the top and bottom with the side seams seam allowance folded back.
Sorry that doesn't even make sense to me- and I know what a mean!

Thanks @cate16 I think I can sort of picture this. I'll give it a go on the next one and hope for some improvement!

This might help
www.seamwork.com/magazine/2016/06/how-to-make-a-perfect-point

In my books it mentions taking 1-2 stitches diagonally across the corner to "blunt" it, in some way this gives somewhere for the bulk to go I think. Described here www.doinaalexei.com/sewing-corner-seams.html. May be worth some test runs!

Thanks @NotMeNoNo, will also be giving this a go!
MN really does cover all the bases!