[header] How to tell a girl she is pretty [title] Pick the right spot. [step] Your compliment might not be welcome if the setting is wrong. Inside the office, at a professional meeting, in the classroom, and even out to lunch with colleagues are inappropriate situations to tell a girl that she is pretty. 
Doing so in these circumstances will put the girl on the spot and could embarrass her, which is not what you want to do. [substeps] A compliment could also seen as inappropriate if you are on strictly professional terms, either by her or by co-workers and friends.