Steps 3 & 4: McCall's 6898

Step 3 Shoulder Seams
Stitch shoulders in a French seam.  Be careful to match the front princess seams to the back princess seams.  Pin wrong sides together.

Below is a closeup of the two princess seams matched.

Press French seam allowance to back.

Note the precise matching of princess seams at the shoulder seam.
Step 4 Side Seams
Stitch French side seams. Press to back.