Well, what have you done? And what genre is the book? My novel is young adult fantasy. So I joined an online YA group, and am flogging to the agents associated there. I also look up agents on line, do a little background research to make sure they rep my sort of book, and to make sure they are legit. Then I send a query letter. So far only one asked to see the manuscript, and turned it down. Pretty typical. It's a numbers game. Flog enough and someone will look at it, and if it really is decent, they may take it.