Hi, I've seen several ladies (professional) wear the "good witch" outfit simply by the choice of clothes they wear...in the good witch case...it would be something white. Then emphasize your makeup and make you a good witch hat to wear.
Another suggestion is to be a "princess". Simply wear something flowie and make you a crown with sparkle makeup!
A "doctor/nurse" outfit is also easy to do.
I always like this type of "costume" rather than the store style costumes. It shows more imagination!