I find the other answers very helpful, and I want to add only a few small things.
It depends on what you want to write, in what form, and for whom.For example: should it be prose or poetry, a short story or a scientific article, a letter or a commentary, or just all of it? Depending on your answer, there are different options.
Reading comparable fonts from a professional pen is useful for gaining a sense of sentence constructions, words, verses, or arcs of tension.In doing so, I would prefer authors whose style you personally like. Scientific articles demand objectivity or objectivity, which is why they usually read relatively monotonously. The arc of tension in terms of content plays a major role here.
For short stories, novels, personal letters, originality is important, which means that you as an author should learn from others, but develop your personal style.This is the only way to make your content look authentic. So you use common and proven professional tools or patterns, but in your own personal way.
What many authors surprisingly often forget is the target audience.Example articles, studies or reports: Who should read this, what expectations does the group of people have, what drives them? Therefore, write from the reader’s perspective by immersing yourself in them. What would you expect in their place? If you intend to convince them of something, what would be the right chain of argument? What has worked in the past?
In the brevity lies the spice, it is always so beautiful.In prose, you can use quite long sentence constructions with many metaphors, unless you deal with them in an inflationary way. In a technical article, sentences should be rather short and concise. Otherwise, at the end of the sentence, the reader has already forgotten the important core message of the initial part. In addition, the author should pay attention to a low “noise ratio”. This means that long sentences with little content seem rather counterproductive. Exuberant descriptions, as in novels, are frowned upon because they unnecessarily strain the reader.
Phrases and phrases with “man” or passive constructions a la “will”, “became” you should avoid if possible.This does not mean that we should no longer use them, but use them sparingly. Such sentences seem distant (man) or slow down the reading flow (will be, was). If such constructions too often follow each other, the writing leaves a very bumpy impression. Unnecessary filling words such as “so-called” or “quasi” also have a bland taste, which is why I owe them in my texts as much as possible, which I do not always succeed in oral communication.
As other forensics have rightly pointed out, regular and intensive practice plays an important role.Frequently, let familiar people give you feedback. Best of all, you ask for feedback from those who belong to the targeted readership. Did they like the written language? Was the text too simple or too complicated? How did they find the chain of argument? How would they briefly summarize what they have read? What do they think of the external form, what about the structure of the content?
Of course, there are specialist literature and audiobooks that deal with the improvement of writing skills.No blanket judgment can be reached on this. Everyone should go to a bookstore or library for a few hours to find books that are right for them.
Incidentally, in my answer, I assumed that the question refers to German as a mother tongue.If you want to improve language skills in other languages such as English, you have an additional hurdle to overcome. The rest, on the other hand, is similar.
Finally, a word on the subject of quotations.Appropriate quotes in the right place are the salt in the soup. Again, less is more. A suitable quote reinforces your content statements with words from your mouth, making your statements more credible. You get a famous personality on board. Of course, there are quotes that have worn off in the meantime because they appear too often. Rather lesser-known quotes increase the reader’s curiosity and attention. On the Internet there are some free sources of quotations, which are usually divided into categories.
So start writing, pay attention to the good tips of the other forists, and on the one hand do not practice too little, on the other hand not so much that you lose the fun.Only a motivated author can motivate his readers.