My friend recommended an excellent book on writing: "On Writing Well" by William Zinsser, and I finally started reading it.
It is a how-to writing book, teaching principles and techniques to whoever likes to take her or his writing to the next level. It's exactly what I need.
More than a year ago, I started my daily doodling + writing practice that I call "A Doooodle A Day". Many people told me that they loved those doodles, but for me, writing is the more important piece. After all, I doodle because I want to write daily -- I can't write easily without some visual elements helping me mark the progress. I enjoy flipping my sketchbook and remember the story I wrote for a specific day.
My improvement on writing is tremendous -- for someone whose native language is not English. Aside from that, my oral English has improved a lot, too. I found it easier for me to chat with people on more topics for a longer time now. I'm very thankful.
However, several things have gradually become bottlenecks for me, like searching for topics to write, how to write it well and how to find interesting perspectives to write about. Now, I don't want to write just for the sake of writing, it's time to learn from writing experts, and get better in writing. As William said: "... with the arrival of the word processor, teocopposite things happened: good writers got better and bad writers got worse. ... bad writers became even more verbose because writing was suddenly so easy and their sentences looked so pretty on the screen."
The journey of improving writing will be long, but I'm sure it will be fulfilling.