Good writers get their meaning across clearly.
Bad ones leave it open for interpretation.
When you write, always work towards communicating your meaning in an exact manner.
Not doing so diminishes your piece, as different readers end up taking away varying things from it.
Every statement you write tries to say something.
Being precise entails making sure that they mean exactly what you're attempting to communicate.
Even the slightest gaffe can affect the entirety of a piece, after all, especially when the misunderstanding comes early or at critical points (such as in the main argument or in the conclusion).
You don't need to make your statements long enough just to fill in those empty spaces in your paper or at your computer document.
To get your reader's interest towards your context, write precisely.
When should you check each statement for meaning? I suggest doing it during the editing and rewriting phases (after doing one pass with your corrective writing software), as focusing on such can significantly slow you down while drafting.
It normally takes a sharp mind to be able to pull it off, so make sure you're sufficiently focused during the activity.
Will you be able to ensure precision throughout the entirety of a piece? Maybe not.
However, if you do edit with the conscious goal of fixing up accuracy, you should be able to cut errors down so significantly that they won't be much of an issue.
Even with a slip here and there, the reader can still gain the bigger picture.