(1) A rough diamond = an uncut diamond ;  a person who has generally good character but lacks manners , education or style.

• My grandfather was a bit of a rough diamond.
• The young actress was a rough diamond , but with some training she would become a superstar.

(2) Down and out = a person without money, a job or a place to live.

• Nobody loves you when you are down and out.
• A hostel for down and outs.

(3) No prizes for guessing = something that is very obvious or clear.

• No prizes for guessing where Daniel is. ( i.e it is very clear where Daniel is)
• No prizes for guessing why Sarah didn’t show up to work on the day after her birthday.