Follow the Leader: John Green's subsequent works tend to have more than a passing resemblance to the characters and plot already featured in LfA, particularly Paper Towns (though that book is an intentional Deconstruction of LfA)
Narm: The sheer amount of Contrived Coincidence that sets up the book's big disaster can be a bit hard to believe. Among several other steps, it involves not one but two missed anniversaries just happening to fall on the same day, as well as a phone call by exactly the wrong person to exactly the wrong other person about exactly the wrong subject at the absolute worst possible time.
Anyone you know could die in a senseless accident and you will never know if you could've prevented it.
Think of anyone you care about. Now think, do you really care about them, or just your idea of them?
Strangled by the Red String: One of the few intentional (and well-done) examples with Miles and Lara. They have approximately less than zero chemistry and hook up without any sexual tension or build-up... but this makes sense. There is no substance to their relationship. Lara appears to take no interest in forming a deep connection with him, while Miles is already in love with Alaska.
It's possible Alaska only decided to try hooking them up because she knew Miles had feelings for her, but she was already in love with Jake and didn't want to destroy Miles in the process. So she picked the first girl who had a crush on him.
Each character gets a turn at this when they play 'Best Day, Worst Day'. Lara had to leave her childhood behind when she moved from Romania to America, Pudge was humiliated in seventh grade and vowed to Stopped Caring (until he came to Culver Creek), The Colonel's dad walked out on him after being an abusive partner to his mother, Takumi watched his grandmother burn on a funeral pyre and Alaska watched her mother die right in front of her, then her father blamed it on her. Ouch.
Miles' epiphany at the very end, particularly the following line:
But the not-knowing would not keep me from caring, and I would always love Alaska Young, my crooked neighbor, with all my crooked heart.