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]
(..) - Hey there. Hi. I'd like a Clabmin fire tea... Budweiser Classics, Cardassian sunrises and... - Try the Slusho, it's good. - A Slusho mix, thank you. That's a lot of drinks for a woman. - And a shot of Jack, straight up. - Make that two. Her shot's on me. Her shot's on her. Thanks, but no thanks. (..)2009 Star Trek