I use a damp paper towel and just wipe it.
Retina shouldn't mean anything as far as I'm concerned since you're not wiping the pixels, but the glass covering it.
And like someone said, if you don't have anything actually sticking on it, and just dust, just take a cloth and wipe it - maybe even blow your breath on it as you wipe, just like you would a phone screen.
If you have certain things stuck to the screen, a damp paper towel should suffice for most occasions.