All you need is one.
I would send down a small ship to land in front of the U.N. building. I would send a message that I would address the world media at a specific date and time.
I would walk out onto the stage, and give a speech to the TV cameras. Meanwhile, behind me, my underlings would be hauling barrels of KY jelly and crates of rubber gloves into the ship.
When my speech was over, I would return to my ship, and return to orbit.
“Very funny. But seriously now, take me to your real leader.”
An alien lands at a gas station and walks up to one of the two-sided pumps. “Take me to your leader,” he declares. “Take me to your leader!” he repeats. Then he says, “Take your fingers out of your ears so you can hear me!”
I’m not proud of the fact that my answer would be paternalistic. I’d “take over” for humanity’s own good. Eliminate the possibility of war, reduce corruption, combat racism and bigotry, etc. I’d govern, more or less the way the British governed India.
It isn’t a good answer. It might even be the wrongest possible answer. But, hey, you asked.
I’d let a few of my spacecraft be seen by military pilots, loners, and crackpots. Abduct and probe random humans. Leave crop circles. But leave no conclusive evidence of my species’ existence whatsoever. We ETs just love to fuck with people.
By accident I tuned into Fox News first. Then I’d leave since there is clearly no intelligent life on Earth.
That’s just foreplay for the tentacle sex.
Euro Disneyland at Paris. It’s the height of human culture. Then leave, with mouse ears.
Make ourselves known and our capabilities evident. Assign everyone on the planet a random number and a short procedure for creating new numbers for new people, then just leave. They’ll be trying to figure it out for generations.
I wanted to go a long time and didn’t get to. So now that I’m an alien with a spaceship I can land anywhere I want I’m going to land it at Gatorland.
Do you know how hard it is to get good Cantonese food on Qzyldrp?
Why would I even bother with earth if I’m so capable?
Though I might just to unironically quote The Lost Skeleton of Cadavra
“Sorry, sometimes my wife forgets that she is not an alien from outer space”
Take in a Broadway show. Hit a blowjob bar in Bangkok. Maybe round it off with Tokyo Disneyland.
We would arrive at Earth, locate the <untranslatable thing> we were looking for, take it, and leave. Nothing more.
After all, if we aliens were all that superior, humans would be unable to do anything to more than annoy us.
Do humans care what ants think? Do humans even think about ants, except in the rare cases of studying them or exterminating them when they are obstructive?
Any bar can make a blowjob. Why Bangkok?
I really want to tell you about -----ing the -----.
They, um, make an “extra special” version there. 
Capture a breeding pool of a few thousand humans from various places around the globe to be sure of having a varied breeding pool, to be transplanted to another planet. Then annihilate the rest, and let the wildlife recover from human domination. Before leaving, upload Wikipedia to preserve a summary of human history and knowledge. Then leave.