When writing characters, remember to consider not only their personalities but their psychological development. Not every character has to fit a completely different temperament profile. It is possible to have two extroverted optimists in the same story and keep them unique by homing in on where they are in life: make Character A young, naive, and dreamy and make Character B wise, determined, and practical.
This would be a good exercise. Pick three or four personality descriptors and apply them to two characters. Focus on differentiating them based on how their age/culture/class/history has influenced their psychological development.