Hallie Ephron (a mystery writer who also wrote a great how-to book) has two piece of good advice for writers that she keeps posted next to her computer. You can read them here.
How do I love dlgarfinkle? Let me count the ways. [Full disclosure: platonically!] She recently had a great post about how to be a better writer, covering everything from starting a book to what to do if your manuscript makes you want to vomit.