What to do if you see an unidentified flying object? Stay out of sight, take a picture if possible, watch, and find out whatever you can without endangering yourself. In case of a First Contact, it's better to learn from others' mistakes than your own.
Movies and TV shows are faulty guides in this case. For one thing, visitors from outer space are unlikely to speak English or possess such advanced translation technology that communication is no obstacle. They are unlikely to be humanoid. They might not even recognize us as an intelligent species. Even if they do, they are unlikely to see us as the rightful owners of the planet. A look at our own history suggests that, whatever their official mission statement, explorers are generally looking for something to benefit themselves.
The UFO may hold a couple looking for a suitable planet to terraform into a wilderness retreat. That would probably mean exterminating the indigenous life forms. Or the space ship may be looking for resources. Minerals, water, plants, living tissue, samples of flora and fauna, maybe even atmospheric gases. Maybe this is a first wave of colonists, looking to take up residence on our planet, as masters, of course, by virtue of their superior technology. If they take pity on us, they might teach us their enlightened ways, soon to become the only acceptable ways. Our lives, as we know them, would be over. And that might be a good thing.
They might be lost, like ET, looking for a way to phone home. If they can't manage, they may be marooned with us, and become Robinson Crusoe, while we play the role of Friday and the cannibal tribes. How would we treat another species that is depending on us for help? It could be our finest hour. By the time those 60 minutes are over, the vivisectionists will have rounded up some funding to study the newcomers.
What to do if you see a UFO? You could alert the authorities. But if you do, you might have to cope with some major ridicule if they actually come to the site and the visitors have left.
You could pray. Pray that there is a logical explanation for the UFO. Pray that you are having a psychotic break. Pray that these creatures really are superior, and will give more than they take. Pray that we don't inadvertently offend them. Pray that they are not immune to our diseases. Pray that it will all work out for the best.
Then take a deep breath, and step into the future.