German is rich in vivid, often literal-sounding idioms. "Ins Fettnäpfchen treten" means to commit a social blunder, literally "to step into the little fat bowl." "Den Nagel auf den Kopf treffen" means to hit the nail on the head — to be exactly right. "Jemandem die Daumen drücken" means to keep one's fingers crossed for someone, and "auf dem Holzweg sein" means to be on the wrong track or mistaken.
Several idioms describe physical or emotional states in memorable ways. "Einen Kater haben" — strikingly, Kater means "tomcat" — refers to having a hangover. "Die Nase voll haben" means to be fed up with something: "Ich habe die Nase voll von diesem Wetter!" "Um den heißen Brei herumreden" means to beat around the bush, literally "to talk around the hot porridge." All of these idioms draw on concrete everyday imagery, which is why they tend to stick in memory once learned.
Colloquial expressions add color to everyday speech. "Schwein haben" (lit. "to have a pig") means to be lucky or to enjoy a stroke of luck. "Jemandem auf den Keks gehen" (lit. "to get on someone's cookie") means to get on someone's nerves. "Jemandem einen Bärendienst erweisen" is fascinating because it means to do someone a disservice while sincerely trying to help, drawing on Aesop's fable of a bear trying to swat a fly from a sleeping friend's face. Mastering phrases like these marks the transition from competent communication to truly idiomatic B2 speech.