Get inside a literary agent's head with this blog:
The agent reps authors who do fantasy novels, but even if you write other sorts of books, this blog will give you an idea of what NOT to do. Funniest pieces involve her ripping apart various queries and manuscripts sent to her by clueless, hopeful writers.
Writing is hard. Not everyone can do it. Even those of us who can (cough cough) have a tough time doing it right. Tidbits like these are most helpful.