"The dignity of movement of an iceberg is due to only one-eighth of it being above water."
There is no substitute for knowing what you're talking about. No writing advice, and no style of writing, can help you write well about something that you have not properly understood. The question, then, is: When have you understood something well enough to write about it?
There is no straightforward answer. In fact, it depends on what you want to say. A simple rule of thumb is that you should never write everything you know about a topic; you should leave a great deal unsaid. Hemingway's image of writing as the tip of the iceberg is apt here: for everything you say, everything you put down on the page, there should be a great deal that is left out, that is not said. Most of your knowledge should be under the surface.
If you find yourself writing a paragraph that exhausts your knowledge on a given topic then it is unlikely to be well-written. Your sentences should always be written in a way that suggests questions; and you should have answers to the questions they suggest. In fact, any sentence that expresses knowledge will always suggest questions. Much of the stylistic problem of writing descriptive prose lies in controlling those questions.
As a writer, you have to make decisions about how to say things and those decisions are best thought of in terms of the questions that the curious reader will most likely be left with after reading what you have to say. We might also say that your problem as a descriptive writer is to manage the reader's curiosity. In a sentence that covers one part of the topic you imply questions to be answered later. If you do this right, the reader feels a series of small but significant intellectual satisfactions.
If you move from one sentence to the next implying only questions you do not answer, the reader will get frustrated. But you cannot, and should not, try to answer all the reader's quetions. The important thing is to be conscious of what questions the reader is likely to be left with at the end of the reading. This is where an imaginary conversation with the reader begins.
You can only make the necessary decisions about what questions to raise, and which ones to leave open, on the basis of deep knowledge about the subject. I mean "deep" in precisely the sense in which all writing is necessarily superficial. If you know only enough to write a paragraph of true sentences about a subject, then you know only enough to a write one good sentence. That sentence should mark the centre of your knowledge, and it should indicate (implicitly, elegantly) fruitful questions for further discussion.