Good writing is easy to learn. You already practice every day, which is a significant first step to get better at it. But it is not sufficient. There are two things that you have to get right to improve your writing skills
You have to care
You have to learn how to recognize feedback
Do you care?
You should be consciously thinking about improving your writing every time you write. It is easy to go on automatic mode, write it all and hit send. You are usually thinking about the issue at hand, not about some meta-awareness of the communication itself. This meta-awareness is not instinctive, but it is necessary.
Keep asking yourself: am I doing a good job with this writing? You can leave all changes to later, editing it after you wrote the first draft. But the caring about the writing itself should always be there.
Do you know when it is bad?
Feedback from your writing is not an easy thing to get. One problem is that you rarely get it at all. Writing is inherently asynchronous, so when people are thinking about your writing, you are not there. And when you do get some feedback for your written communication skills, it is often mixed with feedback about the ideas that your text contained. Feedback for your writing is a very elusive thing. You have to learn how to capture it.
A reliable sign that your writing should be improved is when people are misunderstanding you. Whenever you feel tempted to write "As mentioned in my last email..." consider it as a failure on your side to communicate that. Sure, communication has two sides, and it might be the other side's fault this time. But it is much more productive to be always assuming that the fault is in your side and you could have written it better.
Also, observe when people reply with doubts about what you just wrote. Ask yourself if there was a way for that point to be clarified in the original text, leaving no room for doubts. Again, it is more useful to consider that everyone is intelligent and you could have written it better, than assuming everyone is dumb for not understanding what you just wrote so clearly.
Let your future self evaluate your writing. Now and then, read something you wrote a long time ago. Months or even years ago. You will probably have forgotten the context and all the details of the message you wanted to pass, and have some distance to judge the writing. Do it, check if the message is clear, pay attention if you are having doubts about the message. If you feel it could be better, rewrite it at the spot. It is a great exercise.
Why don't you do it now? Go find an email from more than a year ago. Look for a longer one, with a few paragraphs. Read it, judge it and rewrite it.