Playing golf with clients is one way to 'mix business with pleasure'. [=to do something enjoyable that is related to your work]
I accidentally 'mixed up' the two files. [=I put each of the files in the place where the other one should have gone]
He 'got mixed up in' a plan to destroy the government. [=he became involved in a plan to destroy the government]
(..) buried here as well? No, he wanted his remains returned to Storm's End. - Such a tragedy. - A fairly predictable tragedy. Hunting and drinking don't mix. I should say not. My son's a hunter. It helps him forget he's never been within a mile of a real battle. (..)2013 TvShow: Game of Thrones Title: And Now His Watch Is Ended Season: 3 Episode 4