I used a basic outline off of a costume website for this. In my earliest projects
(I've learned better collar-making techniques since).
Some main things are the use of gussets (triangular pieces of material under the arm) and gores (triangular
skirt pieces for girth on the sides). Also the sleeves have not simply been hemmed, but sport actual cuffs which is an easy
way to add a nice look to an outfit.
I chose the dark blue lining for the collar even though it was not intended to be seen, for the slight contrast
it gave. Always be open to 'thinking outside the box' to make your costumes more unique.
A little bit of wired trim used for a belt and headband top off the outfit.
I found the site whose pattern I based this on. My main alteration was a rounded neckline.