I try to do it before I even touch it. 😊
The best way to do that is to select your next reads by relying on your own previous reading (that gets easier as you read more), or on the opinions or recommendations of people that know you very well or have very similar tastes.
I haven't abandoned a single book in years. The few times I was tempted to throw something aside, it was because I was misled by hype (and comparisons that seemed promising but didn't deliver), or - most commonly - because someone gave it to me as a present.
‘Whatever works’ is always the best rule. I kind of started doing it because I hated going to peoples houses, glancing at every single book in their bookshelves - as every sane person does - asking about a title and hearing ‘oh, I haven’t read that one’.