The subject, purpose, audience, situations, and characters about which you are writing define the context of your book. Be mindful of the situation or environs of your writing. This will help you to stay focused, keep your ideas organized and clear, and develop a product that remains consistent with its context throughout. The result; readers will enjoy your work and they too will remain clearly focused on your purpose.
Discrepancies, even small ones, create discord in the mind of the reader and distract them from the situation of your writing. Everything starts with the subject and purpose, and everything else should be consistent with that. However, as you write, be careful in the selection of words and the meaning they have in the context or situation in which they are used. Consider also the inferences and other thoughts that a set of words or phrase might imply.
The historical context of your writing also determines what you write and the words you choose.
Modern ‘pop’ language that didn’t exist in the 1400s has no place in dialog written for that period. Nor do blue denim jeans and t-shirts. It pays to research the historical context to assure consistency in your writing.
Your writing style establishes the attitude that is conveyed to the reader. Your writing attitude may be conversational, like a fireside chat, or humorous, or more formal and academic. Maintaining a consistent writing attitude is as important in writing as using the first person or third person, or the present tense versus the past tense.
When quoting other famous people, do a little homework to understand their historical context so you use their words in a manner consistent with their original meaning and intent. If you change the meaning intentionally, you might find a clever way in your writing to explain or adapt the meaning to your context.
Technology also has a context.
Don’t write about smart phones in the 1970s. If you describe technology, or automobiles, or weapons or other objects, make sure you are not only historically consistent, but also accurately reflect the true characteristics of that object. That old vehicle may not have had air conditioning before that modern convenience was invented.
Situational context is probably the easiest facet in which to maintain consistency, but it can also be the area with the greatest opportunity for ambiguity. Every passage, set of events, or scenario of a story may include background or environmental writing to set the scene, and the dialog and actions of the actors involved. Read the passages again to look for ambiguities in sentence structure. For example, “He saw the soldier with the telescope”, or specific words that could be interpreted differently.
Sometimes the best detector of these inconsistencies is another pair of eyes, such as your editor, or another good reader that you can rely on. Remember, the answer is never “Of course, I meant this, or that!” If the reviewer came up with a different interpretation, you would be well advised to change it to remove the ambiguity and remain consistent with your context.