Since I took several writing courses, both in high school and college, I find I spend the most time on word choice. In the first place, you want concrete nouns and verbs—words that appeal to the senses, helping you to see, hear, smell, taste, or feel the action. It will save words and that brevity in its very terseness will stress the point you are trying to make. You need to avoid delayers ("there is," or "there are") whenever possible. As their name implies, they delay the point you want to make and that, too, will dilute its power. And you want to avoid passive voice if you can. In scholarly works, or even simple expository writing, that is not always possible, but just a little effort will make your writing much easier to read and understand, and more likely to be remembered.
Don't you wish we had time to edit our spoken words? How many times have I said to myself, "I could have said that in a better way," or "I wish I hadn't said that at all?"
You can see from the above that one of the things good writers try to do is omit extraneous words. The same thing is true for watching your tongue. The Proverb writer tells us that when words are many, transgression is not lacking (10:19), in other words, edit, edit, edit! The less you say, the safer you will be. James tells us how to accomplish that: Know this, my beloved brothers: let every person be quick to hear, slow to speak… (Jas 1:19). Slow down. Listen and pay attention to what you hear. Then think before you speak. You are a lot less likely to need editing.
Whoever keeps his mouth and his tongue keeps himself out of trouble (Prov 21:23).