"Tenga que un buen día."
Is there a general rule for deciding if an adjective should go before the noun or after?
Tenga que un BUEN día.
Es un día AGRADABLE>
Adjectives that precede the noun:
I am sure I am missing a few! These are most probably the most common!
There are also a few adjectives that can precede or follow a noun depending on which meaning you are trying to convey!
Que tenga un buen día.
Have a good day.