Science Fiction author Mary Doria Russell (The Sparrow) has a page on her site with advice for writers. Most of it's not terribly profound: the importance of discipline, perseverance, taking criticism well, etc. But she does say a couple of things that I think are worth repeating.
She quotes a very useful poem by Gary C. Wilkens called "When to Use Colons." I won't quote it without permission, but you can find it in Russell's "advice for writers" link above.
She also supports Neil Gaiman's thoughts on writers' groups. When you first decide to Become A Writer, an early temptation is always to join a writer's group in order to help yourself "feel" like a writer. Gaiman says, "On the whole, anything that gets you writing and keeps you writing is a good thing. Anything that stops you writing is a bad thing. If you find your writers group stopping you from writing, then drop it."
I'd add to that by saying that anything that channels your creative energy away from writing is also a bad thing. Talking about writing can do that. If you want to feel like a writer, then write. I resisted the temptation to join a writers' group because I knew that I'd be doing it for the wrong reason. If a writers' group will truly help you to stay disciplined and keep churning out the words; by all means join one. Personally, I'm with Russell when she says, "It's bad enough reading my own crappy drafts... I don't subject myself to anybody else's. Spend the time making your own stuff better."
Another piece of useful advice is regarding scam artists who masquerade as literary agents. Russell (and every other legitimate agent and publisher I've ever heard from about it) says:
"Legitimate agents make their living by getting 15% when they sell your work to publishers who pay YOU. Be very wary of an agent who charges a fee to read your manuscript. Good agents make money selling properties, not reading manuscripts."
She goes on to talk about a twist on this scam:
"The red flag goes up when any 'agent' suggests that your book is 'almost there' but could benefit from being 'professionally edited.' The agent will give you the names of several book doctors, so it looks like the 'agent' is an honest broker. No matter which book doctor you select, you will be charged thousands of dollars, and you may be sure that part of the fee is kicked back to the agent."
There's more in the link.
And just in case you're curious, here's a message board that talks about where you can find some of these jokers.
Thanks to my friend Shara for the Mary Doria Russell link.