http://spanish.about.com/cs/grammar/a/whereadjective.html It explains that either is fine, but when you put the adjective before, you usually emphasise the state it's in or change the meaning, so I'd be careful about it. I still say go with convention and use "cosas nuevas" unless you really want to stress that the things are new.

cosas nuevas nuevas cosas no se dice... suena mal... en cambio con otras palabras si se puede anteponer aunque el sentido es completamente diferente.

it is better firs because : hay más énfasis en lo que quieres

cosas nuevas