Love of God: I know I have offended God and I want my relationship with Him to be right.
Crisis: An event in my life (brush with death, world event, family troubles, etc.) has awakened in me a need for repentance.
Fear of Hell: I think that if I die I will go to Hell for my sins, so I need to repent.
Conversion I have discovered or re-discovered God in my life, and I want to be closer to Him. I realize that my sins are preventing this.
Other God works in many ways to bring us to Him in repentance. Follow His Spirit.