Someone else may have a method that works better for you and if you do I would love to hear about it. I have been sewing many years and still learn new things all the time.
First, find the shoulder line on your yoke pattern piece. On the picture I have drawn a broken line where it should be on this one. Cut the yoke pattern piece in half on this line.( Of course I haven't traced the whole shirt front and back -- just enough to do the tutorial. The pattern pieces would extend otherwise.)
Next , tape the front yoke piece to the shirt front pattern piece and the back yoke piece to the shirt back piece. Be careful to not overlap the pattern pieces. I use small pieces of tape because you will remove the tape later or cut through it.
Draw a parallel line from the top of the yoke pattern piece where you cut apart the pattern on the broken line you drew for the shoulder line. Be sure to keep the line parallel to the grain line so the shirt stays on grain. Also under the armhole at the shoulder seam draw a horizontal line to intersect with the parallel line you just drew.
Now, cutting on the horizontal and vertical lines stopping just before where the 2 lines intersect-- approx 1/4 inch.
Overlap at the shoulder seam 1/2 the amount you need to remove from the shoulder width. For me the total is 1/2 inch so I overlap 1/4 inch. Tape the overlap . Tape it again just below and just above where the yoke is taped to the shirt pattern pieces. Repeat for the back.
Now since doing this the "slit" below the armhole will pull up and leave an opening. Slide a piece of tissue underneath and tape in place. Repeat this for the back pattern piece.
Carefully remove the tape where the yoke has been taped to the front and back shirt pattern pieces. If you have trouble removing the tape just carefully cut through it.
Finally, tape the yoke back together, again being careful to not overlap the edges.
If you are using a pattern without a yoke and just have a front and back you can use this same method you will just omit cutting the yoke apart and taping it to the front and back.
I would love to hear comments on this method or any other method someone uses. Thanks for stopping by.