I believe that life is too short to read a book you aren't enjoying, but please don't be overly hasty to give up on it, as there are a number of points to consider before forming your own opinion and delivering a verdict.
1: Have you read at least 30 pages of the book? Just because a story doesn't hit the ground running, it doesn't indicate the quality or pace of a book. Give it a chance – who knows where it will lead you.
2: Right book, wrong time. Just because you aren't enjoying a book now does not necessarily mean that you will never connect with it. We all change over time, and teenagers especially change and mature a great deal over a short period. Putting it down doesn't mean you can never pick it up again.
Of course, once you have given a book a chance and you are hating it, put it down. Don't try to finish a book simply because you feel you must. Maybe it was never meant to be. And if that book is languishing on your bedside table with a bookmark permanently residing between pages 30 and 31, take the hint, wipe the dust off and deal with it appropriately (return to library, donate to charity, prop up table leg etc.)
And if you start pointing the finger at me, this is only a guide: just because I loved a book doesn't necessarily mean that you will love it – but I really hope you do!
