Another free way to improve your writing: join a critique circle. I dabbled in a few through Meetup.com (just punch in your city/state and “writing” and you should get some results) and wasn’t impressed, but it’s all about finding a group with whom you work well. I took a fiction writing class in college three times because I knew the instructor was brilliant and that he’d bring amazing things out of the group. I think it’s harder to get this dynamic without an established leader/authority figure, but not impossible.
I’m wary of online courses that cost upwards of $300, but I’m loath to make a snap judgment and say they are not worth it. Has anyone tried an online, paid course?