Is it proper to say " You should wear clothes in layers since it's cold". Or should I say " You should be layered with many clothes". Which is right?
I don't think there is any set manner to express this, LD. It'd probably depend a lot on the situation, what was understood by all parties to the conversation.
The first one sounds fine, LD, but the second one sounds a wee bit odd. I'd say that we might well say,
You should wear layers [of clothing].
You should wear [your] clothing in layers.