A friend of mine was asking me about the query process. She asked if I started with agents in the middle/bottom of my list and worked my way up. I always thought you should start at the top and work your way down. I'd hate to get an offer if I hadn't given my top choices a chance to read my work.
I keep 5-8 queries out at a time. As soon as a rejection comes in, I send another one out. It keeps me sane and focused on the next step.
I also keep all my rejections. It's weird, I know, but one time I went through my rejections and found one that I'd thought was a form rejection. Then I realized it specifically mentioned the reason for the rejection. Sometimes agents will have more than one form rejection. One for weak plot, one for weak characters, one for weak voice, etc... Even though they're form rejections, those can be helpful!
I only have one link to share with you: Why Rejection Letters Are Great. Seriously. It's all about the numbers. And persistence.
And I have a question for you: How do you query? Do you go top to bottom? bottom to top? How many queries do you put out there at a time? And how do you handle those rejections?