How to Create an Instant Bestselling Novel has some good writing tips. Examples:
I notice some beginning writers seem to dislike using “said” and try to replace the word “said” with words like commanded, remarked, uttered, began, etc. Perhaps they feel that too many “saids” stick out. However, you don’t have to be afraid of using too many “saids.” In fact, it is much worse to try substitutions. The best writers use “said” almost all the time and let the dialog convey the meaning.
Use “which” with a comma when the phrase seems as if it could easily be set off with parentheses and make sense. Examples with “that” and “which”: 1) I like dogs that bark. 2) I like the German Shepherd species, which has pointed ears, a tan coat, and teeth that rip.
Halfway down the page he provides his Bestseller Plan:
If the author creates compelling characters and natural dialog, he or she is 90% of the way to success. My feeling is that the way in which a writer writes is actually more important than the plot. Stephen King, who writes so well, could write a novel about a peanut butter sandwich and it would be great.