Select a key that all of the musicians will start out in. The drummer should begin by playing a beat. The band members should then agree that the beat is adequate or instruct the drummer to change it until everyone is satisfied with the beat.
Instruct the bassist to play a beat to the drummers beat in the decided upon key. Once the bass player gets the beat established, the guitarist should then begin playing and adding chords.
Play this way until you have established a regular rhythm and then experiment with key changes by nodding to your fellow musicians, or yelling out the next key change. Play for 15 minutes until your band has established a musical structure.
Write down your key signatures, timings and key changes, breaks in the music and notations that include certain introductions for vocals, lead guitar, drum or bass solos.
Play the jam that you have written as all of the band members read it from the board.
Continue making changes to the board as band members come up with new parts. Let the board evolve with changes as you play the jam. When the jam becomes consistent with all parts necessary to make a song, write them down on paper for all band members to take home and practice on their own.