When it comes to writing, probably the best advice is to plan, plan, plan before you actually start writing. Separating the tasks of idea generation and writing is a good way to think about it because once you have your ideas down, it's just a matter of moulding the words to suit what you want to say. From then you can start the editing process, which is a combination of both idea generation and writing, but by then you should at least have some idea of what your piece is going to look like. Idea generation can also include research, and that research can lead to a mountain of ideas, that even change your original ideas, so it's worth researching too.