I had piles of manuscripts to read, and only so much time in the day. So I had to weed stuff out. That's when I came up with my personal rule that a writer who couldn't grab me in three went to the reject pile. And here's what I meant by "grab me in three:"
Poems got three lines.
Short stories got three paragraphs.
Longer works got three pages or three chapters, depending on the length of the work.
Every now and then, I would have one that didn't exactly grab me, but the writing was good enough that I set it aside to see if it improved beyond the three. Most of the time, it didn't, but every now and then, I came across an inexperienced writer who needed to tighten up the intro (or even eliminate everything before, say, chapter 6 or verse 4) to make a work sing. It didn't happen often, but it did happen.
But most of the time my rule of three held true. If you couldn't grab me in three, your work was not up to snuff. I still use that yardstick to decide on books to read on my own time, and it works amazingly well.