You have a friend starting her first AdWords campaign. What would you suggest about how to choose keywords?

You have a friend starting her first AdWords campaign. What would you suggest about how to choose keywords? 

A) Include more than 50 keywords in 1 ad group
B) Set a theme for each campaign and choose related keywords
C) Keep each keyword to a single word, rather than a phrase
D) Set a theme for each ad group and choose related keywords