Here are a few things I've learned along the way and had to share with new writers.
1.) Don't Read Reviews
Sounds like an odd thing not to do, being a writer. Sure, there may be some gems in the pile of shitty ones, but do yourself a favor and stay away from Amazon, Goodreads and other venues. If you don't, guarantee it'll f*ck you up.
2.) Don't be a Promo Whore
So many newbies are guilty of this. Don't post your book or link on other authors' FaceBook walls in hopes of riding their coattails. It's rude. You will only alienate readers and friends. Also, don't post your link every hour on the hour. It has the opposite effect—people will loath your author name and book cover.
3.) Don't Quit your Day Job
You've published your first book as a brand-new author. Don't expect to get rich or make the type of money established authors do right off the bat. It takes time, commitment, strong backlist, name recognition and branding to reach the level where you can make some decent money. Most never do—so write for the love of it, first and foremost.
4.) Never Sacrifice Quality for Quantity
Yes, some authors write fast...fine, great. But if you start to build a fan base and decide you can pump out drivel because readers will buy your "name", you're playing with fire. They may hang on for a while, but soon you'll be known for poor quality writing and be worse off than when you started out. You should always be growing as an author, improving your work with time.
5.) Don't Burn Bridges
Unless you're Stephanie Meyer, you're going to have to play by the rules. If you piss off your publisher, get on the bad side of author collegues, ignore your fans, or rant about your poor reviews—the writing world will destroy you. Yep. You'll be left with nothing but a stump, with no potential for growth. It's a huge industry, but a surprisingly small community. Reputation is everything and a little love can go a long way :)