When drawing a portrait, the most important part is the eyes. If the person isn’t recognizable from the eyes, there is more work to be done. John Singer Sargent was probably the best portrait artist from the USA (turn of the last century). He said “A portrait is a painting with something wrong with the mouth”.  Apparently, one can have the mouth a little bit off, but my experience is that the eyes must be accurate. Then, if your subject is eating watermelon, the rest is a cake walk! (sorry – i think it is dinnertime at the time of this writing)