I will explain about the workflow that I prefer!
My Workflow usually consists several steps:
Briefing the ideas (by Client)
Rough sketch for the pose with several options
Client picked the desirable sketch
Cleaner sketch update
Client approves or request some revisions. (If client approves, continue to step 6. If client request revisions, back to step 4.)
Outline and base color update.
Client approves or request some revisions. (If client approves, continue to step 8. If client request revisions, back to step 6.)
Rendered drawing update.
Client approves or request some revisions. (If client approves, continue to step 10. If client request revisions, back to step 8.)
Background outline update.
Client approves or request some revisions. (If client approves, continue to step 12. If client request revisions, back to step 10.)
Background base color update.
Client approves or request some revisions. (If client approves, continue to step 14. If client request revisions, back to step 12.)
Background rendered update.
Client approves or request some revisions. (If client approves, continue to step 16. If client request revisions, back to step 14.)
Overall drawing overview.
Client approves or request some revisions. (If client approves, continue to step 18. If client request revisions, back to step 16.)
Done!
Notes:
Client won't be charged for any revisions during the whole process.
Revisions only get charged in step 17 and only for major changes. For minor changes, it won't be charged.