Get Writing has published some mini-courses to help you fine tune your writing. Whether you're a beginner, intermediate, or advanced writer, Get Writing has mini-courses to help you; no matter what your skill level.
I found the exercises covering horror writing very insightful. There are exercises to practice building the action slowly and finishing the story with a horrifying climax.
There are exericises and articles for writing crime fiction and the pro's and con's for using first person point of view effectively.
There's even a section for aspiring script writers.