There is nothing more certain than that you may form what countenance you please.  An open, serene, intelligent countenance, a little brightened by cheerfulness, not wrought into smiles or simpers, will presently become familiar and grow into habit.  A year will with certainty accomplish it. 

Avoid, for ever avoid, a smile or sneer of contempt; never even mimic them.  A frown of sullenness or discontent is but one degree less hateful.