Is it better to memorize the separate kanji readings, or the words that has the kanji in it instead?

I'm studying for the N3 JLPT, and I'm unsure of what way is the best way to study kanji readings. The list of kanji is long, and the list of different words that can be created using those kanji is even longer. Is it better memorize the kanji readings separately, or should I try to learn the words instead?

Is it possible to accurately guess the correct reading for a word that consists of two or more kanji if you know how they're read separately (especially if they have several different readings on their own)? Is there a neat trick when it comes to guessing dakuten?