So remembering that I am part of a Whole so constituted will leave me happy with all that happens to me. And in so far as I have some close relationship with the other kindred parts, I shall do nothing unsocial, but rather look to the good of my kin and have every impulse directed to the common benefit and diverted from its opposite. All this in operation guarantees that life will flow well, just as you would judge a citizen's life in proper flow when he moves on through acts which benefit his fellow citizens, and welcomes all that his city assigns him.
Two absolutes exist.
First, that we are part of the whole Universe (regardless of whether you believe there is a God or Gods or if all of it is just a random conflagration of atoms bouncing around in a constant flux). There is no denying that there are some things ultimately out of your control and no matter how much you love it or how much you complain about it, whatever "it" is, will not change. You simply must accept it. Stated differently, amor fati. In Stoic terms, this falls under the discipline of desire.
Second, we must recognize that humans are different than the vast majority of other living organisms. What makes humans unique is our ability to reason coupled with our ability to be social. To a large degree, we have a duty to be social - to help others where we can. This duty to help others falls under the Stoic discipline of action.
In my opinion, these two core ideas and disciplines are akin to the two great commandments in Christianity: 1) love God and 2) love neighbor. And as long as we can keep these two ideas in the forefront of our minds and attempt to live accordingly, our "life will flow well" as Marcus states above.
(see also Citadel p. 43-44, 241)