Obtain a standard hymnal from your local church or purchase one online. Any hymnal will work, but you may want to choose a hymnal that is geared to the institution at which you would most likely be hired. Spiral-bound hymnals will rest easily on the piano music stand and the pages can be flipped quickly.
Select a hymn you wish to play. Good choices include hymns for Christmas and Easter, as these are the most commonly requested hymns. Take at look at the parts. If this is your first introduction to four-part writing (the type of composition method in which hymns usually appear), you may be surprised at the complicated nature of the piece. By simply approaching each staff as a separate piece, you will be able to eventually combine each into one piece.
Once you have selected a piece to study, set your metronome at a comfortable pace (typically quarter note = 80) and begin playing. As you progress in your practice session, adjust the metronome to different tempos in a wide range. For example, if you would like to accompany a congregation in a church setting, you should be able to perform the hymn at 10 beats per minute below and above your selected tempo to allow for variations in congregation singing speed.
Do not simply prepare one hymn during your practice sessions. To become a well prepared accompanist, you should practice multiple hymns of different styles until you are comfortable playing them at different tempos. If you are asked to play for a church or choir, you will typically receive the hymn list or music in advance. Play through the hymns or music every day before your first rehearsal (or church service) to be prepared to perform.
Accompanying on the piano is not limited to choral settings. To become a well prepared accompanist, you will need skills that involve successful accompanying of wind instruments. To begin this aspect of accompaniment preparation, obtain any piece of solo literature (for an instrument other than piano such as trumpet, clarinet or trombone) that contains a piano accompaniment. Also obtain a recording of this piece.
Prepare the accompaniment part exactly how you would prepare a standard piece of solo piano literature. Constantly consult the solo part to gain insight into performance techniques. Sometimes, solo parts and piano accompaniment parts will vary in stylistic and dynamic approaches. Your playing should always reflect what the soloist is playing. After the part is prepared, play along with the recording to get an idea of the correct stylistic approach. Ask a friend to prepare the solo part at the same time.
If you are able to find a friend that can perform the solo part, the most valuable portion of your training will be to accompany an actual soloist. As part of your practice session, ask your friend to join you on the solo part. Whatever tempo the soloist wishes to take will be the tempo at which you must play the piece. This is why practicing the piano part to every piece of solo literature at different tempos is important.