Sew the gore/sleeve parts to the body of the tunic.
Sew down the underseam of the sleeves, to the underarm. Stop here. Do not cross the gore/sleeve seam. Tie off your thread and flip the seam allowance over.
Now, starting on the gore side of the seam allowance sew from the underarm down the side of the gore to close the tunic.
By not sewing across the gore/sleeve seam this allows a greater range of motion without having to have a gusset.
 |  |
Hem the sleeves and bottom of the tunic. You might consider finishing the seams using a flat-fell seam (as shown to the right). This makes the seams lie flat so that the garment is more comfortable against your skin, and so that it hangs correctly.
You can also use this same pattern to make your overtunic from. Follow the same directions. When you have completed construction of the garment, decorate the neckline, cuffs, and bottom hem with embroidery, trim, or paint. See attached sheet. 