trick of the trade
A piece of expert knowledge; a smart, quick, or skillful way of working at a trade or job.
Mr. Olson spent years learning the tricks of the trade as a carpenter.
Any one can learn how to hang wallpaper, but only an expert can show you the tricks of the trade.
A smart and sometimes tricky or dishonest way of doing something in order to succeed or win.
The champion knows all the tricks of the boxing trade; he knows many ways to hurt his opponent and to get him mixed up.