Talking about this recently with another editor, we concluded that if you asked 30 editors for the ten worst new writer pitfalls, you'd get 30 different lists. I have enough material to post a new pitfall every month for the foreseeable.
First time writers who know their story and characters well, and want to get to grips with the story, and want to get to the end of the book, are making a strong start. However the same writers can and will make a whole range of errors because of this strong start.
To assume is to take something to be so without evidence. Assumption (in spite of what your management training textbook might have told you) is not always bad. Indeed for a creative writer it is often essential. However there are certain assumptions that are almost indistinguishable from hope.
The author who wants to get to grips with his story as fast as possible will often assume that the reader will recognize the world of the book, and consequently he will forego description. Knowing his characters and locations well, he will omit to portray them to the reader - especially since he may find this a tedious distraction from moving the plot along.
If the characters are well developed in the author's mind, then by the end of the story the reader will have got to know them quite well - though not without a little frustration. If they are not well developed ...
Of course, exactly the same effect can arise when the author has done no preparation at all in conceiving characters and locations.
Literary commentary that purports to tell you how to write well is always open to debate, disagreement and controversy. A good storyteller can make almost anything work, and anything described as a pitfall might, in the hands of a skillful writer, be viewed as a strength. This disclaimer notwithstanding, the new writer would do well to seek to develop his skill by understanding his weakness.