I've been given some books on writing through the years, but never thought much of them. I didn't read these full articles, but what I saw looked good: Article 1, Article 2 (mostly contains links to other articles on the topic).

There's a lot to consume there in terms of writing theory, but one of my favorite exercises is taking a certain writer's style, identifying some of what is interesting about their style, and applying it to your own writing. The writing needs to be something connected to you and it helps if you can pick a topic that evokes emotion in you, even if it's otherwise not something you consider to be a notable story. The important part is being able to tap into your own vulnerability because it can help what you put on paper to be genuine. This doesn't mean everything you ever write needs to be this way, it's just helpful and a good place to start and learn. It's the whole idea of "putting your heart and soul or a part of yourself in your writing" but that people sometimes talk about. Once you learn to tap into that and break down the barriers, you can channel yourself into other writing much easier. Writing like you naturally talk can help, but it's probably bad grammar for writing (except when writing conversations).

Again, it's not always easy and I have no clue how much harder this is if you live somewhere without native speakers in the language you are writing, but you need others to read your work. That's what most writing is for!

If you end up doing technical writing for science or similar, my best advice is keep the layman in mind. Most science writing is overly clunky and full of jargon and buzzwords that not only drive off the layman, but drive off scientists not in that particular field. It's stupid and bad writing all to stroke the ego of the writer to get a false sense that they sound smarter. To many, it just makes the writing hard to consume. Technical writing should go into sufficient technical detail while aiming to be as easy to consume as possible, even if you make assumptions that the audience understands a topic. Here is an example of good technical writing.