Explanation: A musical arrangement only works if it can be performed. Think practically about what each player needs to create their part. Put it in writing. Print music for each musician. For some, it will simply be a list of chords or a lead sheet. For others, it may be a full musical score.
Many a song arrangement gets abandoned the moment the recording begins. Usually that's not a good thing. At the very least, make sure that the players have the roadmap when they record. If you are going to be paying for studio time, think of how much money you'll save is each player nails their part in one or two takes. The more specific the material you give them, the faster and better they will play.
You may also consider creating a CD or tape of their parts so that they can practic at home.
Next: 14. Practice and perfect your lead vocals