Depends on what kind of person you are talking to. If the individual is tolerant of philosophical conversation, begin with the absolute nessesity of self-ownership, which should be the least difficult. From self ownership, you can discuss libertarianism's idea of justice, and also validate the existance of private property. Once you have done this, everything else, all other subjects, are deducable. Example: How would a consistent philosophical libertarian view national soverienty?
Also, here is a heirarchical list of words to use, ordered from worst to best.
Capitalism<Free Market<Open Market<Voluntary exchange/ Voluntaryism/Free Exchange
Turf/Territory<Ownership/property<Fruits of labor.
As you said, it would be better to refrain from attacking socialism at the beginning, and indeed you should lay out the philosophical basics of libertarianism. Decentralization should be viewed as simply a logical result, not a pillar of libertarian philosophy IMO.
GOOD LUCK