I have seen little green aliens in lots of places (Ads, cartoons, magazines etc.). I remember a Tom and Jerry TV movie featuring attack on Earth by little green martians. Other examples can be the Martian villain from Dan Dare and Zirconians from Aliens in the Attic movie. You can also see them in Farm Invasion USA game (Android/iOS).
I think, those little green aliens are icons in Sci-Fi culture. So, I never needed to give examples.
Here are features they usually have:
They are small varying from 1/4th of adult human to the size of finger. I don't need to define it strictly. You know what it means.
They always have one kind of spaceship. The little saucer with upper dome transparent.
They are green, blue kind of color. But, if the idea was originated from different color ones (but I highly doubt), that would be acceptable.
They are funny and annoying at the same time. They may not try to actively annoy you, but their even serious actions (like scanning you) can annoy you (like scanning gives you shock or makes you naked for an instant). Although, this may not be true.