How can I discern the specific calling of God on my life?
The Bible expects us to walk in the good works that God has prepared beforehand for us (Ephesians 2:10). And Romans 12:2 says, "Be renewed in your mind so that you can prove what is the will of God"—His will, I believe, for you—"what is good, acceptable and perfect."
First, I suggest that you give yourself to the word of God. Immerse yourself in God's assessment of you and the world, so that you see things through God's eyes.
Secondly, get a realistic view of yourself—your gifts, weaknesses and strengths—and let others help you by participating in the Body of Christ and having them comment on what things they see in you.
Third, look at the situation in the world, either in your immediate vicinity or in some distant place, and get a burden for the world.
I believe that when these three things happen—saturation with the Bible, a true understanding of yourself, and a clear vision of the needs of the world—and you begin to stir them together with the stirring spoon of prayer, I believe that what will emerge is an aroma of what the clear calling of God is on your life.
You'll know which way to follow God and use your gifts for him, whatever the particular specifics are.