When sewing seams, there are two steps. First, prevent fraying by finishing the edges with a zigzag stitch. Then use a regular stitch to sew the pieces together.
In the seam allowance, use a Marks Be Gone pen to mark the location of the hip line.
To finish the outside edges of the seam allowance, sew a line of zigzag stitches, then iron.
Matching the edges of the seam allowance, right sides together, pin the pieces together.
Start sewing the seam with three or four back stitches.
Remove the pins as you sew the seam.
Finish the seam with three or four back stitches, then press the seam open.