Having read the Epictetus' Manual, considered an important book in Stoicism, here are some common themes that I've observed:
Having a strong internal locus of control is important to understand what is in our control and what isn't.
"Within our power are our own opinions, aims, desires, dislikes—in sum, our own thoughts and actions"
A fundamental concept and perhaps the most important thing I have learned from stoicism – it's less about the actual event than the story you tell yourself of the event.
"People are not disturbed by things themselves, but by the views they take of those things."
Before getting into something, if you're realistically aware of the consequences, you'll be less perturbed by what actually happens.
"For instance, if you are going to a public pool, remind yourself of the usual incidents"
If you believe something won't work, it probably won't end up working. Your beliefs are self-fulfilling prophecies.
"The only thing that can impede your will is your will itself."
Don’t expect the same outcome without putting in the same amount of work.
"Do not expect to equal anyone in effect without putting forth a similar effort. A person who rarely leaves home, who doesn’t converse with, praise, and encourage others, will not attract friends."
"If someone tried to take control of your body and make you a slave, you would fight for freedom. Yet how easily you hand over your mind to anyone who insults you. When you dwell on their words and let them dominate your thoughts, you make them your master."
People usually associate stoicism mistakenly only with this one concept, but it's so much more.
"Wish only that the best team or athlete wins. Avoid the extremes of elation at a win and devastation at a loss."
"Black and white thinking may seem powerful in speeches and debates, but real life is mostly gray areas"