This is an interesting question indeed. I started this post back in January and just now getting around to writing more about it. I have several thoughts on the subject, however for the sake of attention span and time, this post will be brief.
It might be easy to figure out what exactly we are meaning by "ministry." One of the common misconceptions that we have in our day and age is that there is such a great divorce between "ministry" and "daily living." This mindset can be very problematic and have terrible consequences in all areas of our lives. My friends, if you are a banker, you are called to the ministry of doing everything that you can to represent Christ through your integrity, through sacrificial living for the good of others, and being the very best, with Christlike attitude, seizing every moment of every day to live in such a way that Christ is seen as glorious. Another way of saying this is simply, you are called to "live out the Gospel" in every relationship. (I would personally suggest a really good study of the book of Galatians for further assistance with this).
Those things being said, every single believer, whether you are a high school student, doctor, public school teacher, mechanic, waste management specialist, police officer, fireman, computer programer, you are called to the ministry. Every single person who is called by Christ as one of His children, is "called into the ministry." Yes, there are some of those who are going to be "teachers of the Scripture" who are going to make their living by being supported by others, but this group of people in no way are doing anything different than what you and I should be doing. Their gifting and calling is simply different. When you and I realize this, it will free all of us to minister every day in whatever context we find ourselves.
Those items being said, what are some practical ways that you and I can prepare for this ministry for which God has called all of His children? First, God calls all of His children to seek Him first, and His righteousness. Our daily lives should be filled with prayer and radical holiness. Keep in mind what is holiness. Our example - The Lord Jesus Christ. I would suggest a good and complete study of his public ministry. Then ask yourself, questions such as "if I am to live like Christ, how does that work out in my life?" For instance, Christ did not seclude himself to studying the latest Piper book over coffee at Starbucks, going from there to a conference on indigenous world missions, to come home and then to debate others on theological correctness, then from one "fellowship" to another. (Please understand that this is obviously being overstated to paint a picture...I certainly believe that everything just mentioned, in their time and place, are good and profitable efforts). Christ DID spend so much time, not participating in the sin of the world, but he did spend time associating with those whom the world rejected as "lost causes" and "filthy" so much so that the "religious" wanted to kill him and made false accusations against him.
My final comment on this, with hope to follow up soon on other practical steps is this. If you and I want a recommendation on how to "live out the Gospel" then I can offer you and I no better book than the Gospels. I can offer you no greater example than the Lord Jesus Christ himself. There is no greater teacher than to take a long hard look at His life and ministry and then, by God's grace, walk in the reality of your identity as a follower of Christ.
In all things...Christ preeminent!