on Jane Friedman site:
When you start querying agents about your book, very quickly you’ll discover their guidelines ask for “comps.” Comps stands for “comparable titles”: books that might be considered comparable to your own.
For many writers, coming up with comps is a daunting enterprise, but the important thing to remember is their key purpose: to show where your book would be shelved in a store or who your most likely readers are. Everyone from agents to publishing sales people to booksellers will have an easier time understanding what your book is like or who it’s for if a comparison can be made. “If you liked X, then you’ll like Y.” It also shows that you know something about the current marketplace and how your book fits in it.
On my quest to write the perfect query letter, I got stuck on what comps to use. I channeled my frustration into research. Here is what I learned from the experts.