Read his writing carefully--and read as much of it as you can. Observe patterns, particularly in your experience reading it. Notice the way you feel as you read his work--the entrapment in "The Metamorphosis" and the frustration in "The Trial" are reactions Kafka intended you to have.
Learn about Kafka's life. No one writes in a vacuum, and the fact that Kafka was a Jewish German immigrant growing up in Prague who lost close family members to concentration camps certainly plays a role in his work. Research his mental illness and health problems and note possible connections to his writing.
Consider political and philosophical influences on Kafka's writing--particularly existentialism and anarchism. Freud and Marx had a prominent effect on his work.
Interpret Kafka as a magical realist. Note how his writing conforms to this literary genre. Also consider conventions of modernism in his writing.
Accept that while you can learn more about Franz Kafka, you can never fully understand him the way you could understand a simple poem or morality tale. Kafka's elusiveness is an important part of reading his work.