King Ralph prepares to welcome another king from Africa but forgets
his welcoming lines and says:
Come on, Ralph! You've got a good thing goin' here.(You'll do a good deed or sth important?)
Don't blow it!
Usually, "You've got a good thing goin' here - Don't blow it!" refers to an opportunity for personal gain - not a chance to do a good deed. It sounds a lot like the former Governor of Illinois when he was recorded talking about the "goldmine" that existed in his opportunity to sell Obama's Senate seat.

All Ralph needs to do is to kiss up to the visiting king a little bit.
Thanks, Avangi!