Generally speaking, many Protestant churches have no other requirement outside of a statement of faith by the individual seeking baptism. This practice corresponds to various accounts in the book of Acts, and the baptism happens immediately after the people believe.
But when they believed Philip preaching the good news about the kingdom of God and the name of Jesus Christ, they were being baptized, men and women alike. Even Simon himself believed; and after being baptized, he continued on with Philip, and as he observed signs and great miracles taking place, he was constantly amazed. Acts 8:12-13 NASB
And he ordered the chariot to stop; and they both went down into the water, Philip as well as the eunuch, and he baptized him. Acts 8:38 (Ethiopian Eunuch)
“Surely no one can refuse the water for these to be baptized who have received the Holy Spirit just as we did, can he?” Acts 10:47 NASB (Cornelius)
Some denominations, however, practice infant baptism. For these, of course, the only requirement is that the parents bring the children to be baptized.
I know the International Churches of Christ once required a certain level of discipleship prior to baptism, as they held to the concept of "disciples baptism" rather than "believers baptism". Oddly enough, they believed that baptism was essential for salvation, but would encourage some people to delay their baptism until they were really ready for that commitment, which seems counter-intuitive if eternity is, indeed, at stake.
There may be other denominations that require something akin to confirmation prior to baptism, but I think it would be difficult for anyone to know the baptismal requirements for any and all groups.