It's easily done, of course. There are so many elements to think of when you're writing a novel or other piece of fiction, and it's hard to keep track of them all.
But each of these elements is essential to get right - they're like pieces in a jigsaw, and unless all the correct pieces are present, and they all fit together smoothly, the result won't be a pleasing unified whole.
However, I absolutely don't want you to get too caught up on these to the point of paralysis. That is absolutely not the point of this section.
Indeed, as explained in Writing Your First Draft it really doesn't matter how bad your first attempts are. Making the project perfect (or as near to it as possible) is the purpose of the editing process.
Having said all that, here's a list of the things to look out for - just check out the menu on the right.