The contents of the mind are within our control, whereas the outside environment is not. Stoics become happy by focusing on and learning how to control their internal state, no matter the external state. Once this control exists, the outside does not matter anymore. Happiness – or a stoic calm and peace – can be achieved anywhere, at any time. This is the ideal to strive for. The ideal of the Stoic Sage.
An important tool in achieving such a state, is the ability to change perspectives. In anything bad can be found something good. You always have things you can be grateful for, things that you can appreciate, things that could get worse, things that you can focus on that make you happier than you otherwise would be.
Dwell on the beauty of life. Watch the stars, and see yourself running with them.
Worrying about what will happen doesn't make sense. If it happens, it happens, and the internal state is still within our control. We know that we will die, but that doesn't mean that we can't control our response to that fact. And live, despite that knowledge. Making things matter, internally.
Pain and happiness are just states made up by the mind. Contents of mind, that disappear. Illusions which, if closely looked at from different points of view, completely disappear. There is always a choice. We can interpret differently, disconnecting things that happen around us, from our response to them. And that choice is up to us, we only have to make it.
The stoic choses the response of inner peace and equanimity.
When you arise in the morning think of what a privilege it is to be alive, to think, to enjoy, to love ...