Agents are tough...a fact that I am slowly coming to grips with. Perhaps it isn't that they're so tough as much as they're tough to read. There are very few definitive lines of right and wrong when searching for an agent. Do they represent the genre you're so vociferous about? Yes or No, fairly simple. After that, it's like swimming in the ocean after nightfall. There's no north or south, east or west. You have no idea what's above or beneath you. All you have is whether or not your head is submerged.
That leaves a lot in the way of knowing how to proceed.
Sometimes agents want a query that is detailed and follows a precise formula. Others simply want a letter that is entertaining (I prefer them, personally) and shows that you are a captivating author who can spell and use proper grammar. So, how does one navigate such a task? Lots of research for every, individual agent, tons of patience and tolerance, and--as I'm in the throes of literary battle myself--a thick hide.
So in the words of Dori the fish (Finding Nemo): Just keep swimming.