How do you sew a 90 degree corner?

How do you sew a sharp corner?

Trim: Trimming away excess bulk is always a great way to help the fabric lay smoothly. Grading the seam will disrupt a sharp under layer edge. Sew across the corner: The layers of the seam allowance need to fit into the inside of the corner. The smaller the corner the less room there is for the seam allowance.

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