When writing a novel a good memory is vital. And more than anything else what you must remember is your own work. The character who limps on page six must limp again on page one hundred and fifty, unless you can explain it away. And if you do reference that limp on page six, you need to reference it again, or else why mention it at all? Likewise, the character that has a strong sense of smell should react (when it is there) to either sweetness or something foul somewhere. More subtle characterization will enhance your characters as you build upon consistencies. I am not referencing foreshadowing here, but depth of understanding.
That said, as you build your story, you can add these elements retroactively. That is, you are on that page one hundred and fifty, and only then realize it would help if you went back to page six to introduce some key element. Your reader will never know you’ve done this—nor should they. On the contrary, they will appreciate the totality of your creation.
No one, no one, writes a book from start to finish without going, to some degree, backward. It’s a way of turning hindsight into foresight.