I often click based on voice; not necessarily a direct quotation, some of the best clickbait for me is a cleverly phrased summary. Not actually the summary in this case, but "The Death of a Soul, A Blowjob Beneath a Table, and the Rain of Toads That Followed" made me click on Harry/Draco, a pairing I'd previously avoided.

The thing that puts me off most is spelling/grammar mistakes, or lack of summary altogether, though usually tag forests will have already put me off such works.