I usually ship witht he box lid turned inside out. I go to the dollar store and buy my brown wrapping paper (way cheaper than at the post office) and then I tape down the deliver info on top with packing tape. Then I wrap the ENTIRE box in wrapping tape, to the point that it's pretty much waterproof. I use pretty much an entire roll of packing tape (which also costs a buck at your local dollar store).
I've never had anyone complain about my packing jobs, other than it takes them too long to get through the tape
. Never had any complaints of goods arriving damaged, though.