When I hear of someone who likes to write or ponders becoming a writer, my advice is "just write." Write regularly. Write in a journal, write a blog, write into a computer document.
What do you write? Most times, writing daily is a good way of purging the brain. It's like venting on paper. You write your feelings, inspiring thoughts, reinforcing affirmations, about your day, or about a topic of interest.
You don't have to have a result in mind when you write; not like at school where you write because you have to to get a mark. It really doesn't matter what you write each day. No one will be marking it!
An amazing thing occurs when you go back and read your notes. Your notes may inspire you. They might become the basis for a blog or article. They ground you. They tell you how far you've come.
Compiled, your writing may become a good eBook one day. All writing is valuable--either as a personal release or when used to help another person.
Another amazing thing is you get better at your craft if you develop it over time. I've been going back and editing old articles and sometimes I just shake my head. Some of them are lousy-looking now.
HOW TO IMPROVE
If you get to the point where you want to submit work, you will read submission guidelines. You might also read samples of work. If the submission guidelines are thorough, you'll pick up tips of what not to do. If you submit to an organization that screens the work, feedback from an editor may be helpful.
Courses have value that isn't necessarily obvious. I took a copyediting course thinking I might grow the simple editing/proofreading business I had. I learned that the editors in that organization edit to the "letter of the law." They reference all types of "official" rule books that ongoingly change their rules. To be an editor of that caliber takes far more commitment than I'm interested in.
But what was interesting was how the course helped me improve my writing. Through the lessons I learned things I'd never known. I also used a critique coach. I picked up a few things from her, although some other things she commented on were maddening. In all these situations, I've learned to take away the good and dispose of the bad. No writer needs to feel discouraged. A lot of writing is subjective anyhow. There are new ways of writing that old school writers may not embrace and pick you apart on in a critique. Be wary, and test your gut reaction. If God has called you to write something, do it.
Sometimes harsh critiques can force you to make harsh changes to your manuscript that are needed in a good way. Sometimes they push you to write as an effort to prove yourself. Sometimes the critiques give you the impetus to move forward in spite of what you've been told.
Personally, I think there are too many wet blankets out there. We are in an era of innovation. Writers usually have a strong need to express themselves, like I am doing in this post. If I worried about all my punctuation and proper phrasing all the time, I'd get no where.
So find expression. Forget about perfectionism. If your piece is to be bought, it will be bought. If someone thinks it stinks, fine. Let them have their opinion. Just do your best work, have fun, and go for it!