The first stage is organising yourself - I'm not talking about outlines, character descriptions or anything like that. This is about setting schedules, looking at deadlines, being realistic about what you can achieve (while doing everything else). If you have a writing partner this part would involve ensuring that you get time to discuss and do whatever you need.
Then comes the actual planning. Yes, I know some people don't plan but honestly there are very few professional and successful writers who don't. At a totally random guess I'd suspect it was in the ratio of about 50:1. Like all good statistics that was completely made up. It may be an underestimate.
So planning, outlining, character descriptions, treatments, synopses, loglines. They all belong here - everything except the actual writing thing. It may be that you need to get approval on the various stages that you are at. if you do well it's the earlier logistics phase that makes sure you organise yourself to make those deadlines and make sure you get the feedback you need.
This is one reason why it's important to get things clearly stated, if not legally stated. Your agreements must be based on the client actually doing their bit as well. If you don't get the feedback then you can't proceed. But if you then get blamed then that's not good. You need to be sure that you've a clear picture of what you need and when, and you need to demonstrate reasonable efforts to get the client to supply their part of the deal (in this case: notes).
One job that I did that went wrong I was writing A/V narration for educational videos (among other things). The client did not deliver any notes and then complained that it wasn't right. We parted company but I knew, and could prove had it been necessary, that the fault lay in the other camp. I had made plenty of reasonable efforts to get the feedback. I didn't get it, the job became late and that was that.
Finally you have the writing. The actual getting those words down on paper ... well, screen. Whatever.
So is that it? Oh dearie me no, not at all. Two more episodes to come.
What's on the turntable? "Mademoiselle Will Decide" by Jools Holland and his Rhythm and Blues Orchestra, featuring Mark Knopfler