Listen to a recording of the song that you wish to arrange. Make note of the instrumentation in the arrangement and how it differs from the instrumentation of your band.
Using recording software or pencil and staff paper, write out all of the percussion parts and chord changes in score form (one on top of the other with all measures lining up). Assign the chords to the piano or guitar player.
Assign each major component of the percussion to a different instrument. For example, bossa novas have a 2 + 3 or 3 + 2 clave (repeated rhythmic motif), which can be given to the conga or clave player. If the recording has a drummer, the drummer would also be playing eighth notes on a symbol. These notes can be assigned to a different percussionist in your band, such as the maraca player.
Decide on a rhythm for your bassist. Some genres of Latin music, such as tango, have a standard rhythm. If this is the case, you should not deviate from the rhythm since this is what will alert dancers to the genre. If there is no standard rhythm, try to have some of the bass notes line up with the percussion section and others not line up with it.
Write out the vocal part if the song has lyrics. Be sure to consider your singer's vocal range.
Arrange the horn parts. At least one horn should be playing the melody if there is no vocalist. If there is a vocalist, have the horns play complementary parts. Transpose horn parts where necessary; for example, trumpet music should be written one whole step above concert pitch.
Decide on an appropriate tempo for your song and write that at the top left corner of each instrumentalist's part. Write the time and key signatures on each part.