Over the years, I've seen these techniques work, and I'm sure you have too. Success is almost guaranteed - although you might never know about it. Going viral is actually quite easy, and it will cost not a single cent.
Open a door for someone. They might thank you, they might not, but the easing of their way will ease something from their mind, even if they barely notice it, and the next time they come to a door, or a possibility in a conversation, or a moment when they can ease someone else's thoughts, they might very well open it for another person. And that person, eased, may do the same for the next person, and they for the next ...
Say good morning to the bus driver. Say good morning to the check out operator, the ticket dispenser, the woman making your gingerbread latte. Acknowledge other people, let them know in this simple little way that you see them as part of your community. Then notice how the person behind you will say good morning too, and the person behind them, and how soon everyone is smiling. Good manners can be contagious.
Share something of yourself. You have a thousand tiny stories behind your eyes. They are gifts you can give the world. How you found two four leaf clovers in the garden. How a bird sat on your hand to eat breadcrumbs. How a man in a meadow played pipe music for you. Tell your tiny stories so that other people think of their own stories and wonder if maybe they could tell them too. Before long, more people are sharing themselves, and the community is enriched with all this secret beautiful magic.
Make people laugh. These are dark days. We can't all pass important laws, or address parliament, or grow our own food. But we can be a moment of simple joy for others. Share a joke and see how far the laughter ripples. Maybe it will go all the way around the world.
Pass on what you know. Notice I didn't say teach. I am an old hippy, I have an aversion to people setting themselves up as teachers (except for, you know, actual teachers). Simply share your knowledge. It doesn't really belong to you anyway. It was given to you - passed forward by another person, or unfolded for your understanding by the benevolent universe. Pass it on. And on it will go, and on.
Appreciate others. It could very well be that we're here in this world, in this way, because we can help each other. Not one better than another, but everyone different, with something unique to offer - a brilliant theory on quantum physics, a perfect scone recipe, a gentle smile, the height to reach a tin stored on the top shelf, artistic talent. Everyone is important. Everyone is special. Give what you can to others, and appreciate what they give to you.