I do lots of writing and here is how I do it.
First, I do what I call the brain dump. I just get all my ideas on paper as quickly as possible. At this point I am not trying to fill in the ideas with context, just get out the ideas.
Here is an illustration to help you understand what I mean. Imagine you are gonig to call your friend on the phone. Before you make the call you have in mind the ideas you want to discuss during the call. But, you do not write out a word for word script of everything you will say. You fill in the details and the context for the idea while you are talking.
So, the brain dump is just to get the ideas on paper. Format doesn't matter, you can use bullet points, numbered list, roman numeral outline, whatever.
Second, I do what I call the ten percenter. Now, I take the ideas and put them into some kind of order. I give the thing I am writing a title. I give it a table of contents to the degree that I can, the table of contents at this point will be incomplete but I don't care. Then I arrange the ideas into sections, what might be chapters in a book or section headings in a white paper. Now for each idea I write one paragraph. Then I add an executive summary and a conculsion and a bibliography and an index. I create a glossary of terms at this point.
When the ten percenter is done now you have your book / paper / article. You are just missing the context and the details.
So take each idea and fill in the details. Make sure that you have a paragraph that puts each idea into context of the whole and that ties each idea to the previous and next idea.
I find that this approach helps me take something that I view is overwhelming and break it into manageable pieces. It gives me a place to hang everything, then I just have to expand on the the details.