In order to perform karma yoga, there is a simple general principle to keep in mind: bring a third component into every action. If, for example, you are digging a ditch, there is you who is digging the ditch, and the ditch which is being dug. Now add a third focus: say, a disinterested person who is seeing you dig the ditch. Now run the entire action through his head while you are digging. It’s as simple as that.