This is probably the most terrifying question you will ever face. Here's how you handle it.
  1. Shrug and go, "Everything's been great", but then mention a few bad things that have recently happened so you don't seem too braggy
  2. Say "Pretty good, how about you?" Then when the other person starts to tell you about themselves nod and say "uh-huh" a lot until it feels appropriate to talk about something else
  3. Provide a very specific account of exactly how you happen to be feeling at that given moment (try to touch on your states of being physically, emotionally and spiritually); delve deeply into as much personal minutiae as possible
  4. Launch into a long, detailed description of every minor career triumph, disappointment and general meeting that you've experienced since last seeing this person (this is the preferred option if you work in show business)
  5. Just start quietly weeping
  6. Yell "Good!", then quickly walk away and move to a new town