You know karate? Time to learn CA-RAZY! lol
The internet is your best friend if you want to know, so just google "boxing technique" or whatever you want to know about.
Try to let him make the moves. Its about dodging and then striking, but that might be hard without practicing. If you think he can box then get in close and bring him down.
If you can keep moving you should be ok. Keep the fists tight and strong, pull your punches, chin tucked in, arms up. If he swing either move or block. Judge his punches. If he lands a bunch right away and you think you won't be able to hang, then just clinch and bring him down and settle it there.
Good luck, hope you don't have to end up fighting.