1. *There is nothing glamorous about writing* - I learned that the hard way. It's work, just as sitting in an office in front of a computer for eight hours a day is work - in fact, almost *exactly* like that (except that at the end of a month in the ofice you get a paycheck, and a full-time writer, well, doesn't). It sometimes might be highly ENJOYABLE work, if you have that kind of bent, but it's work. At least if you even aspire to a professional status, it is. If you don't, well, NONE of these rules would really apply to you, then.
2. There will always be those who think that you might be marginally insane if you admit to hearing voices in your head - but hey, it's not a bug, it's a feature. Being in touch with your characters is pretty much half the job of writing a good story.
3. There will always be someone whom you will envy. If you get a chance, tell that person so. Don't be surprised if they are astonished to hear it - and don't be surprised if that person then tells you whom THEY envy. We are all colleagues - but at certain times of our development in the craft there will always be someone a couple of rungs ahead of you on the ladder of success. It's actually okay to admire these people. They teach you a lot, and they do it painlessly - all you have to do is read their books.
4. There will always be someone - often published - whose work you will look at and cringe, or stand in a bookstore with a book in your hands, having just read an unspeakable first sentence which would have rendered your own work unpublishable, and screaming at the heavens, "WHAT WERE THEY THINKING? AND IF THIS GOT PUBLISHED WHAT THE %#$@((*^%* IS WRONG WITH ME?" That's okay. These moments are invaluable. This is the "I can do better than this" moment, and it has spawned many a fine writer in its time.
5.When you DO get published, don't sit back and expect the world to beat a path to your door and lionise you. It might happen, it happens to a lucky few, but for most of us publication turns out to be not so much as a destination as a bridge - to the next book. Dick Francis once said, "i always feel ambivalent when someone tells me that they loved my last book, and devoured it in a single afternoon - that book took a year of my life to produce, and it was consumed in the blink of an eye..." You can only write so fast, and your reputation doesn't so much depend on the book that you just published... but on the one that you will publish next.
And over and above all of this - unless you really are just writing for the joy of it and not aspiring to publication at all - you have to love this whole lark, all of it, the joys as well as the blood and sweat and tears. You have to WANT it. If you find yourself muttering about the torture of it all, if ever you SERIOUSLY ask yourself the question "Why the hell am I doing this" and actually MEAN it, well, there are plenty of easier ways of earning a living.
Not one of them would have brought me any joy.
That's why *I* am still here, still writing. Still in love with words.