...if you're writing a query. There's two kinds of help readily available on the Internet(s): what to do and what not to do. A couple of "what not to do" links:
First, an amusing collection of query fails from an agent in Slush Pile Hell. Go back and read some of the archives, too, they're seriously funny. But also kinda sad...they're all real.
Second, here's some recent advice from agent Jessica Faust about queries: Query Don'ts. Gotta thank @GailCarriger for directing me to it via Twitter.
Sticking with Ms. Faust, here's her deconstruction of a successful query letter for a mystery novel.
Then, I highly recommend joining the Absolute Write Water Cooler. Lots of published and soon-to-be-published writers there, and it's a very helpful community. They have a Share Your Work forum which is behind a password wall, so that the work doesn't show up on search engines. Inside, there's a lovely room called Query Letter Hell where you can post your query letter and get feedback. It can be brutal but it's helpful—you'll get a response and personal attention that agents and editors never have the time to give. There are many success stories in there, too—writers who got partial and full requests from agents and representation as well. Hope it helps.