There are no clear indications on the score of the United Methodist Hymnal as to recommended introductions. Therefore, I use what I feel is best for the specific hymn. Many time this is the last 1/2 of the hymn. Sometimes, it might be the first stanza or two. And there are a few where the entire hymn is played for an introduction as the hymn might only be two lines. I will slow the end of the introduction and pause before the start of the first line. I also change registration (sound of the organ) which, too, is a good tip off. Please view a few of the videos which better show the introduction.
Worship Leader: Please play these through before the service so that the introduction is clear to you and the congregation will follow you when you start singing.