Splitting work to Backend and Frontend

Hello everybody, I am a Fullstack developer and has been as such since the time I began programming. Now recently we started recruting only frontend/backend developers and I have been tasked with interesting task. I have to divide all of our task and split it on Frontend/Backend and I have been wondering how to create a good workflow, that would enable for new developers to eventually become self sufficent.

Can you guys please give me some examples how you are splitting work between Frontend/Backend in you organization? Do you prepare documentation in advance or after specifications (ie. after backend developer does his job)? What do you do with your tasks that imply full stackwork (ie. add new table, add api endoints, and table on the frontend to show the data)? Split them into subtasks? Who then oversees such tasks?

Thank you in advance.