I've had a general frame of mind when writing that I used when writing papers in graduate school, when writing memos as a lawyer, and in writing adventures. It's a fairly simple way of viewing a writing project, and I wanted to speak about it in reference to adventure writing.

Your adventure is a skeleton, or it's a zombie.

A skeleton has a solid, visible frame. You start with an outline, and the outline is detailed enough to hang all the "meat" on: you know what encounters are going to happen in what locations, and in what order you're going to present them (which might not be the order the PCs encounter them, of course). The hard part is getting these good bones in place, because filling in the rest requires some attention and time, but it isn't often very hard. If you're writing this way, do not be afraid to take as much as a quarter or third of your writing time preparing a good outline. Have other people (beyond your developer) read and comment on your outline. Wrestle with plot details right in the outline (like "what clues lead the PCs to the abandoned mill?"), rather than addressing them later in the text.

A zombie consists primarily of chunks of text taken from someplace else reworked into an adventure. Most often, a zombie adventure is one that I'm adapting from another edition, so the bulk of the text already exists but needs some modifications. Sometimes it will be a compilation of other adventures, scenes, or ideas that need to be stitched together. In other cases, I'll have encounters, scenes, or even whole dungeon sections that are all written up, but they need stitching into the rest of the adventure. I often write such scenes when I'm on vacation, or otherwise away from my work computer, and then I've got a 5000-word chunk of work to stitch into my adventure. The most important thing to remember for this is to save a lot of time at the end of the process to read and re-read your adventure. Have others read it specifically looking for jumps or gaps that don't make sense, because zombie-written adventures are prone to those. (I'm well aware that stitching body parts together is more like a Frankenstein's monster than a zombie analogy, but the "skeleton vs. zombie" idea stuck in my head way back in law school, and it's that way in my head now!)

My strong preference is for writing adventures as a skeleton rather than a zombie. My adventure outlines are sometimes as much as a full quarter of my word count for the whole adventure, which means my skeletons have particularly thick bones, I suppose. Others may feel more comfortable with the zombie approach.

The most important thing, whether building like a skeleton or a zombie, is the review at the end. In the best of work, it probably isn't clear whether you wrote it as a skeleton or a zombie--it's just a delightful monster.