1. Do I have a hook?
Also known as the elevator pitch. Can you summarize your story into one sentence? Is it an interesting sentence? Is it so interesting that it would stand out among a pile of thousands of other queries? Your hook needs to clearly state the conflict and the stakes. A man is about to commit suicide when an angel shows him what his town would be like if he had never lived. What's the conflict? A man is so tortured (doesn't matter by what) that he wants to end his life. What are the stakes? A man's life and apparently the future of an entire town. Who are the characters? The man, the angel, and on the periphery, the entire town (they'd have to be otherwise who would care about what happened to them, right?).
2. Do I have a platform?
It used to be that you would have to publish some short stories in respectable magazines or journals before you had a real shot at an agent. Nobody offers that advice anymore--because most of those magazines and journals are now defunct and even if they weren't, the book buying public sure doesn't read them. These days you need to have an online presence, you need to be able to reach thousands of people, and you need to prove that you're not going to fade into the night. Taking the time to keep up a blog and a decent webpage is a wise investment.