Okay, admit it. There are occasions when you've eagerly started reading a bestselling novel (that you've plunked down $30 hard-earned dollars for), and been wildly disappointed. Maybe as you flip through those pages, you see unrealistic plotlines, paper-thin characters, endless cliches, bits of stilted dialogue, or even poor basic language structures.
Then, admit this. Your next thought is: I could write a story/book better than this one. WHY is this person published, and I'm not?
The interesting thing is that we, as writers, can actually learn something from these poorly-written, how-on-earth-is-THIS-a-bestseller books. We can learn what NOT to do in our own writing.
For instance, when I was a student getting my teaching degree, I learned a heck of a lot about what makes a good teacher by watching good teachers. It makes sense. But - I also learned a lot about what kind of teacher I did not want to be, by watching the less-than-great teachers: overly-harsh, overly-critical, insensitive, aloof, uncaring, or boring.
I like to apply this to writing, as well. When I pick up a book I'm not particularly fond of, one that has (in my opinion) tremendous flaws, I don't stop reading right away. I try to learn from it. I study the flaws, study how they're made, then make a mental note to avoid them in my own writing.
You can learn almost as much from a bad book as you can from a well-written book. Not that you should waste your precious time purposely seeking them out, of course. But on the hopefully-rare occasion that you do run into them, take a little while to study them - and to figure out how you don't want your own books to be.