Drawing a nail is fairly simple. Female fingers are typically slim whereas male fingers are more thick. Of course, a female may have a thick finger when she is either a) portly (obese), or b) she is masculine in nature. Don’t forget: an obese person’s finger is more rounded.
As for drawing a nail, the length may vary from very short to extremely long. If you look at the examples to the left, you’ll notice that they also differ in shape (some are pointed, some curl underneath itself, some widen outwards, etc).
Drawing a finger at the side, you’ll notice that the nail goes downwards midway. Notice also that the nail may slightly go up, slightly go downwards, or go straight.
Drawing a finger from the top, the nail is basically a simple shape: triangle, rectangle, square.
Since the nail begins several centimeters from the end of the finger, the nail will shorten considerably when drawn (and viewed) from the bottom.