As things stand, we rely on words to convey thoughts from one person to another. In everyday speech, we value fluency more than structure. But written language requires more stringent standards. If you don't understand what someone has said, you can always ask for it to be repeated. The two main components of good writing are clarity and imagery.
Clarity means concentrating on the meaning of words and avoiding ambiguity.
Imagery means choosing words and phrases with the power to evoke something in the reader's mind. Think of your writing as a cruise missile. Clarity is the navigation programme. Imagery is the impact when it reaches the target. It is relatively easy to fall back on vagueness and ready-made phrases.