One of the things I like about Lisa Gardner's website is that she includes a link for aspiring writers called WRITER'S TOOLBOX. There's some great stuff on there, so take some time to check it out. She has published many books (both romance and thrillers). She sold her first novel when she was just 20, and her latest novel Love You More comes out next month, March 2011. She has 12 New York Times bestsellers and won The International Thriller Writers award for her novel The Neighbor.
She sent along some advice that's short and sweet but certainly relevant:
My best advice is to sit at your computer and write. Every day. Get to know your market and go for it. You can’t get rejected if you never submit. Those rejection letters are just more steps on your path to publication.