How can your friend prepare for lifestyle changes involved with quitting substance abuse?

use regular reminders of personal motivations like family, career, and health
reserve treats or rewards for when he is no longer tempted to do drugs
create a cover story to tell friends and family so they do not know he is in rehab
keep his schedule and friends as consistent as possible to avoid too many changes

Use regular reminders of personal motivations like family, career, and health.

Or

Keep his schedule and friends as consistent as possible to avoid too many changes

I was once a drug addict, and both of these things helped. Keeping a tight schedule and sticking to it really helps, especially in the beginning. And Using regular reminders of what you will lose/ and what you want for your future are both ways that really helped me.