How to get to know your market

You don't necessarily need to know the future, per se. Just look at Amazon, see what's coming out, and see if you can find trends. Also, there are probably posts on here, blogs, etc. regarding new trends. You don't have to be an expert, just show that you care enough to look. It's more about placing yourself in the field than knowing statistics. Here's an excerpt from my query:

"Recently, "boy" books like Jake Wizner's SPANKING SHAKESPEARE and John Green's PAPER TOWNS have gained incredible popularity, and I believe that's because the fit in a vein that is under-represented. While books by authors like Maureen Johnson are
expertly written and hilarious, boys often won't read books with pink covers and girls on the front."

It's a double edged sword, too.

I'm also studying agents, and find posts from two years ago saying "The vampire thing is pretty much played out." The best agents are more concerned with new, fresh stories than trends. (So sayeth I, and so preacheth the Query Shark.)

If JK Rowling had stuck with trends, we wouldn't have Harry Potter. Same with The Temeraire series - which has done really well, despite everyone spouting the end of the dragon reign in fantasy.

What I do, is read my genre. Not hard. I love fantasy. Amazon is a good source to know what's coming up and out as is http://www.fantasyliterature.com/ They have a tab for "New Fantasy Releases".

I don't think agents expect you to know the ins and outs of the publishing world the way they do. I do think they can reasonably expect that you are well-read in your genre and know what are the popular trends. So you if you are writing paranormal novels for young adults and have never heard of the Twilight series, that's a problem. That doesn't mean you need to fit to a certain standard, I just think they expect you to know a little bit about where your book fits into the market. I suspect a lot of the agents who make this request have done it after signing authors who, it ends up, have basically lived in a cave for the past ten years and have no clue about what's popular or what's going on in their genre.

I don't think any agent worth working with is going to expect a newbie author to have a total marketing plan in place; it's more just a general familiarity with what's out there and what the trends are, and being a regular reader and bookshop browser should do the trick.

Subscribe to Publishers Marketplace. That way you know what's selling right now, not what sold two years ago.

I attended an open pitch session at at UK conference last year. One of the questions the panel consistently asked was 'what books that have come out in the last 5 years would you compare your work to?'

look at the other books in that genre that are out, and are coming out. look at the writers, check thier websites to see what they are working on, look at what sold well, check bestseller lists, prize lists. go into waterstones and see who has the most shelf space.

now try to work out where your work fits into that.

Also keep an eye on the best-seller lists, particularly USA Today and Publishers Weekly. Watch those lists long enough and you'll see the titles and authors that generally do well.

Also, if you aren't already, read books in the genre you're writing. The more you know about your genre, the better you'll be able to compare your work to others, so that you can tell the agent or editor, "My book is like X author or Y series only different because of ABC."