I always consider the providence of God when asking what God wants of me. God is in charge, God is all powerful, all knowing.
With this, God does not need us to do his work. He can spread the gospel in many ways, and he does, but we know that he uses us to do it, and he uses us in many ways.
He gives us various talents and circumstances, so that no one of us is any more equip to spread the gospel than any other of us, who are willing and who have lent themselves to the purpose of God's will.
So, when you think of it like that, spreading the Gospel is not so much of a duty as it is a privilege. How will God use you? is the question to ask, not so much, what should I do for God?
The will of God, or the will of man? Our will is worthless, and dangerous and sinful. It is not righteous. God's will is the opposite of our will.
Why do I say this? because I think it's the most important thing to consider when living the Christian life. The giving up of our own will.
We can not be in the will of God and our own will at the same time, I believe. I think there are many Christians with the best of intentions, who are living for God with their own will.
They think they have to be a preacher, start a church, pass some good moral laws for the country, write some books, perhaps lead others in worship or start a Christian rock band :p......What ever it is they are wanting to lead the charge up the hill for God, but there is often more to their efforts than God. They seek recognition for their efforts.
If Christ appeared before you and gave you a choice of the doing the most glorious thing for his kingdom, or the lowliest of things for the same purpose; which would you choose? It's a rhetorical question really, but the answer should be neither. The response to God should be; do with me what you will, not what I'd will of myself.