In fiction, the first few words or letters of a chapter are often either capitalized or formatted differently. Make these words consistent with the rest of the text. This may require changing the text to sentence case and re-capitalizing anything that needs to be recapitalized (such as proper names). We do this because some screenreaders read UPPERCASE words as separate letters (i.e. U-P-P-E-R-C-A-S-E) which sounds like an abbreviation and is annoying.
Excerpt of a book where drop caps and capitalization should be changed to sentence case: Drop caps and capitalization
Headings are an exception. All uppercase words in headings tend to be read as words, but if you want to change it, use capitalize each word or Title Case.
In one unusual case, an author capitalized each word as a stylistic choice (e.g., "Once when I answered that Emily Dickinson capitalised, Mrs Quinty told me Emily Dickinson was not A Good Example, that she was a Peculiar Case, and the way she said it you knew she regretted it right away…"). In a situation like this, leave the text as-is.
For example: #thisisanexample should be changed to #ThisIsAnExample
Another example: PHRASEINALLCAPSWITHNOSPACES should be changed to PhraseInAllCapsWithNoSpaces
Q: There is a name in my text that appears as follows: Richard III. Should I change it to Richard the 3rd?
A: No, TTS is smart and will pronounce it like "Richard the 3rd" :) Most always, we avoid editing the original writing in any way. We can change how the TTS pronounces words by adding specific tags into the code.