If it is not right, don't do it: if it is not true, don't say it.
Your impulse on every occasion should be to a complete survey of what exactly this thing is which is making an impression on your mind - to open it out by analysis into cause, material, reference, and the time-span within which it must cease to be.
Realize at long last that you have within you something stronger and more numinous than those agents of emotion which make you a mere puppet on their strings. What is in my mind at this very moment? Fear, is it? Suspicion? Desire? Something else of that sort?
Giving others the benefit of the doubt is a mark of a Stoic. Marcus details what this looks like. Someone does something wrong. First off, how do you know that it is wrong? The first step, therefore, is checking your assumptions. And then, let's suppose indeed the person has done wrong. Do we also know if he or she has already beaten themselves up about it? Maybe give them a break before condemning them. Then there are truly, indeed, bad men. Don't be surprised by this, just as you would not be surprised that an apple tree grew apples. And if you really wanted to help a bad man, then attempt to smartly do so.
How much clearer can Marcus be in chapter 17 of Book 12? If it is not right, don't do it. If it is not true, don't say it.
The goal of the discipline of assent is to ensure your impressions exactly match reality. Therefore, reserve immediate judgement of events. Instead, take time to do a full assessment and analysis: what is it made of, what is the context, how long will it exist? Always going through this removes emotions and strips away false impressions. Fear and anxiety and exuberance and haughtiness vanish.
(see also Citadel p. 40-41, 287)