The other night, my son asked God, "Do you want me to have a dirt bike?" He then looked over at me and informed me, "He said yes." Wow. I'm so glad my boy can so clearly discern the voice of God. Don't you wish it was as easy for you to discern God's call for you in life?
How can we discern the voice of God? When we are "listening" for His call, where might His voice show up?
In your prayers...this will require you to spend time with God, not just laying your requests before Him, but listening for His requests of you.
In your Bible...God often speaks directly to you with the exact words that He spoke to someone else in Scripture (this is one reason why Bible reading can be so exciting, and not just a religious duty.)
In your church family...this side of Jesus Christ, we have access to the divinely called body of Christ. We are supposed to discern God's will in community, not in isolation (notice that this requires you to have intimate community with friends of the faith...that wasn't an accident on God's part).
In your circumstances...you can't discern God's call by interpreting your circumstances exclusively, but God will always support His calling for you in this world's events.
Notice what is not on the list..."it will be reasonable to you". God never asks for what is reasonable. He asks for faith.
Remember this: if you don't know your calling, it's not because the Caller isn't doing His job. It's a listening problem.