Actually writing down things. I was scared of putting my work out there because I have pretty thin skin. But I thought, "hey if I want to improve, I actually have to start improving, ya know?" and just threw out my first episode. Every episode after that I just keep on looking at my dashboard so I can get a taste of tasty, validation. So every update is a constant struggle with my confidence.
On a less meta note, my novel challenges me by seeing how I can keep characterization consistent and believable, and not just all over the place (I'd like to think that I'm doing an ok job at it, but really, that probably isn't true). Same with the dialogue, I hope my interactions with people were enough to make it seem believable and not stiff.
Also, keeping my writing from sounding like a boring academic paper, which I hope I'm improving on!