Well, I am not a writer, but from what I have read, there are all kind of writers. Some take ton of time and have the whole book (or series) ready before writing a single word, while others plan as they write. They all go through revisions though, and everyone say a good editor is really important.
As for writing long form, I recall reading someone's opinion that you should start with short stories, instead of writing full length novel or long series from the get go. This was more about when you are honing your skill, instead of your first published work, from what I recall, but that is one person's opinion in some specific context (that I don't completely recall) so take it for it's worth.