Though meant for creating subtitles for foreign users, this link of TED was quite informative for my purposes—deciding line breaks for two/three-line-per-page stories for children. It’s less grammar based and more aesthetic based.
A few important rules I understand from above are:
- Do not break up linguistic units among lines.
- Maintain balance, similar length, between multiple lines. Maintaining line-length balance is more important than keep linguistic units together.
- When absolutely necessary to keep linguistic units together (like a person’s name), then the line break should still not cause a line to be more than 50% shorter than the other line.
Further quotes from above link:
The articles (a, an, the) are never followed by a line break.
An adjective should stay together with what it is describing, but two or more adjectives can sometimes be separated with commas, and then it is possible (though not preferable) to break a line after one of the commas.
Clauses should stay together (never break lines after relative pronouns like which, that, who, etc.).
Prepositions are not followed by a line break if the break would separate them from the noun they refer to. A preposition in a concrete/physical meaning (e.g. "The book is in the drawer") always precedes a noun, and cannot be followed by a line break. However, in English, a preposition that is part of a phrasal verb (put up, figure out, take in) may sometimes not be followed by a noun ("I figured it out yesterday"), and so, it can be followed by a line break.
Proper names should stay together if at all possible (think of them as a single word with many parts).
Grammatical style guides don’t seem to cover the rules for line breaks, but another link might help
Important paragraph from above-mentioned link:
Oxford says in page 140 that "Do not carry over parts of
abbreviations, dates, or numbers to the next line", "Do not break
numbers at a decimal point, or separate them from their abbreviated
units, as with 15 kg or 300 BC. If unavoidable large numbers
may be broken (but not hyphenated) at their comma, though not after
a single digit: 493,|000,|000."