Here's a good quote from Stephen King: "The road to hell is paved with adverbs." I like that one a lot, and it has certainly helped me with my dialogue.
Another really crucial pointer for me that I came across in a literary mag I subscribe to, bluntly stated - and I'm paraphrasing - "Don't assume that your reader is an idiot." Basically, stop over analyzing and over describing and over explaining every little detail in hopes that the reader will be able to follow along. This will have the opposite effect and most likely make them stop following along and close the book.
I admit that my shortcomings - when it comes to writing - are partly due to the fact that I hated reading when I was younger. But now I have to accept the fact that, although most book readers might be socially inept, they usually are bright and like to figure stuff out for themselves. (Sorry, that's the jock in me talking ;D)
Prior to this realization, I had completed a rough draft of the first 19 chapters of my book. After having done lots of reading about writing, I have now eliminated at least 1000 - in some case several thousands of words - from each chapter! Yikes. My book is tentatively planned for 30ish chapters, and in nineteen I had 92,000+ words! A seemingly unbearable task to follow, since this is the first book in a series of six. My poor reader was getting spoon fed to death.
Now my writing feels much better; more natural. It's also taking less time, now that I know what to look for, and these re-writes have become quite enjoyable. I'm just dying to get this stupid thing finished though, so I can submit it and get on to other projects I'm excited about.