I've got two exercises that have really improved my writing. I call the first one 'ten ways' I write a scene ten different ways, each time changing the scene dramatically. Sometimes I find one version is exactly what I wanted and go with that. Others I blend several of the versions to create the winner.
The next exercise I use is to take a section, a scene or a chapter from a book I really admire and write it several times. I really dive in-depth to the word choices of the author and decide why they picked that word. Then I rewrite that section using my own voice and word choices. I find that the two apporaches can usually solve any problems I encountered between any given scene.