from Nikki Magennis
1) Write poetry. Poetry can help a writer focus on rhythm, sound and pacing and encourage you to be rigorous about your word choices at a sentence level. These skills will spill over into your other writing, too.
2) Record conversations. Real life dialogue is a fascinating, messy beast. I love writing and reading transcriptions, and it'll help your dialogue to look closely at how people really speak.
3) Edit. I'm tempted to write this for the last three points, but that would be cheap, so I won't. But let me say as strongly as I possibly can that every piece of good work has to be edited over and over again, preferably with a bit of time lapsed between drafts so you can come to it with fresh eyes.
4) Find at least one good beta reader. Critting other people's work as well as sharing yours with peers is scary, dangerous and invaluable.
5) Never stop questioning everything, particularly your own work. I've been writing professionally for years and I still feel like a shitty beginner. This is good. I hope I always feel like a shitty beginner - 'may my heart always be open to little birds', to put it more poetically. You should be constantly challenging yourself on all fronts - whether on subject matter, style, structure, form, purpose. Everything.
More of Nikki's work can be found here: www.nikkimagennis.com