As you write your query letters to editors and agents, you want to showcase how your story fits within the current market. This is also a chance to really showcase how your story is competitive and why the editor or agent would want to read more or sign you as a client. Of course this is really a difficult challenge because you are trying to keep the initial query short and sweet. One of the best ways to work around this is through using "Comps" or Comparable Stories to show a bit more of your project.
Essentially, "comps" are stories from other established authors that you can say your story is really similar to. This might be similarities in terms of themes, characters or voice. When you do this, you are essentially riding on the coat-tails of the other author.
For example, you may have written a women's fiction piece about a couple of women trying to find their place in the world. Together, the two of them learn things about each other and about themselves through their adventures. This is a pretty common trope. But you can add to this by saying it has similar elements as seen in something like THELMA AND LOUISE or BOYS ON THE SIDE. Using these give the agent or editor something that he or she might be able to relate to.
But here are some things that I want you to consider.
First, you have to take the time to explain WHY your story is equal to those projects. If all you have is that these are road trip movies and your story is to, that is not enough. Show us a bit more in terms of depth talking about themes or messages.
Secondly, make sure that you are picking projects that are pretty familiar. While editors and agents do read, we might not be reading that obscure Argentinian author from the 1960's.
Finally, make sure that your comps are not all over the place. You will notice I used two similar movies to make the comparison in my example. What I see a lot of is something such as:
My story is very similar to the Harry Potter series, Gone with the Wind and Sponge Bob Squarepants.
Now, do you have to include comps? Absolutely not. If you really cannot make a comparison, then don't force the issue.