Buy a pack of A4-ish whiteboards. Like these, maybe. Get a pack of Command Hooks. Get a box of large paperclips like these ones I use. Choose your own whiteboard markers. Choose a calendar at Vertex42, download it and print it off.
Decide what you need to keep track of. What’s on deck right now, what’s pending, things to do that you don’t want to forget about, your call sheet, project statuses, availabilities, things you’re waiting to hear about — you decide what you need to be aware of at a glance.
Stick the Command Hooks to the wall. They go on easy and come off easy. Put a clip on the top edge of a whiteboard in portrait orientation. Hang it off a Command hook. Keep going until you have as many whiteboards as you want. Clip the calendar together and hang it off a Command Hook.
If you’ve got the space, get yourself a great big central whiteboard too. But those cost money and the headline is On The Cheap. This is, really, everything you need to run a writing career aside from your main writing tool and your notebook. You can get fancy with filing information and “productivity” systems another time. Get started with analogue and the essentials. And some music.