To start, I always look at the structure of the sentance: exclamatives, commas, colons, ellipsis- all these things can really help you analyse a sentance. For example exclamative indicates someone is shouting, and ellipsis might indicate confusion or a sense of uneasiness.
Then, consider what kind of language is used- formal/ informal register
What kind of words are used? descriptive
Who is the person talking to: can you guess their relationship by the tone of the words or the punctuation?
are there similies/ metaphors/ adjectives - that imply something that might happen later on in the book?