As a boarder, be sociable? (3,2)
I believe the answer is:
get on
If this is the answer I cannot explain how the clue works.
Can you help me to learn more?
(Other definitions for get on that I've seen before include "Advance; prosper" , "Board vehicle or make progress" , "Make progress or advance in age" , "Make progress or climb aboard" , "Age; prosper" .)