Place a few wrinkles at the bend of the arm to make sleeves in a garment apparent. This may seem a slight detail, but it is not unusual that a sketch appears to be sleeveless because of the omission of this detail.
If a garment is trimmed with buttons, count them and sketch the same number.
A few points to bear in mind when sketching a dress on a figure are:
Where is the neckline - high? low?
Has the costume a collar? What shape?
What style of sleeve - short? full? tight?
Has it a normal shoulder line? Exaggerated? Slanting?
Where is the waist line? Above or below normal?
Has it a belt? Tight-fitting?
What type of skirt - circular? Pleated? Straight?
How long is the skirt?
What type of trimming has the garment?
What is its fabric?