Different churches and denominations have different procedures. Here's a brief outline of my own experience of becoming a Methodist minister:
Having decided fairly firmly that I wanted to enter ministry I began attending the local Methodist church. I did not say anything at all about ministry for several months. Then, when I was sure that this was right for me, I had a quiet word with the minister who was very encouraging and supportive. In the British Methodist church the first step to ministry has to be becoming an accredited lay preacher, a process which will take at least one year, often much longer because it involves studying and passing exams as well as developing the skills involved in leading servies in church.
I began as a lay preacher "on tiral" in 1982 and was fully accredited the following year. I then applied, through the local church circuit, to be considered as a candidate for ministry. This process involved appearing before various assessment panels at all levels of the church from local to national. I was finally accepted for ordination training in 1984 and allocated to theological college in Cambridge for training which included studying for a degree in Biblical Studies at the University. I was ordained in 1987 and took up my first post as minster of a small group of Methodist churches in County Durham.
Becoming a minister is a long process - don't try to take short cuts because both you and your church need to be very sure that this is the right thing to do. And play down your experience as a JW - it won't count for anything but it might work against you!