Step 1: Getting ready with the materials to sew
White fabric for collar
Pattern for a blazer and skirt
http://www.simplicity.com/p-5832-misses-miss-petite-sportswear.aspx this is the pattern that I used.
White trim for the hat
1 gold button
... then any fun accessory/prop for that vintage look.
Lay out your pattern for the blazer and the skirt - cut out then sew your 2 basic pieces for the costume. For the white collar, I just used the same pattern piece and cut it out with the white fabric then attached it to the finished jacket - so easy!