Hmm, aim for younger people.
Simplified German for foreigners (its how many of my relatives speak and while not correct, its good enough for communication:
"Wo ist Gebraucht_bücher_laden?"
"Dort zum Hafen?"
Always append "Bitte". Germans love politeness and it will increase chances of getting an answer. In fact, without it it's downright rude. Maybe that's why :)