One of the most common mistakes is using different narrative languages. Similarly, using different time patterns on top of each other. Such errors are quite technical and are likely to be corrected towards the end. However, if a single expression language is used by taking precautions at the beginning, the editor's process will be much easier and take a short time.
Apart from such technical mistakes, there are not many mistakes when writing a novel. After all, writing a novel is also an art, and it is not very logical to find fault in art.