This is a difficult question to answer. In my experience only a professional editor or publisher can tell you when your book is ready. Many details that the average writer knows nothing about will affect readiness. These include:
- Overly wordy copy
- Rhythm of the sentences
- Clarity of sentences and paragraphs
- Originality of material presented
- Presence of the author in the writing (do you get the sense that an individual actually wrote this?)
- Overuse of adjectives and adverbs
- Purple prose
- Use of powerful verbs and nouns
- Repetitiveness
These items can affect the readability of the book's content more than the facts presented. If the prose is awkward, your reader will notice the writing, not the information you present. This you don't want.
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