Well, since we were talking about names, while I’m pretty sure they’re not required for the JLPT (you’ll just be told a name’s reading if it’s necessary), if you feel like it, you can find a list of the most common family names in Japan and study those (here is one on Wikipedia, and here is a post where I’ve broken them down by reading).
Yeah, but only as a guide. There’s unfortunately about a thousand and one exeptions, like 川口, which uses kun’yomi despite being two kanji placed side-by-side, and 信じる which uses on’yomi despite appearing to be a verb stem (etymologically, it’s actually the noun 信 plus the verb する… and actually, 信 doesn’t even have a kun’yomi, so that one might be a bit academic).