Answer by Claire J. Vannette:
Step 1: Decide which girl you would like to understand.
Step 2: Ask her lots of questions.
Step 3: Listen to her answers, and clarify anything that doesn't make sense.
Step 4: Supplement with your knowledge of human psychology and your experiences with other people.
Voila. You now understand a girl as well as she can be understood. When you'd like to understand a different girl, start over at Step 1.