The other day, here in the US, a man came to my house to be paid for some work he did in my yard. We chatted for a few minutes, then, as he was taking his leave, he unexpectedly kissed me on the cheek.
Later I realized the reason behind his action: he knew that I was French and that the French greet one another by kissing, and he wanted to thus show his knowledge of the world!
What he did not know is that we French women do not kiss our painters, plumbers, electricians, or gardeners, -- unless they happen to also be our friends of course. Otherwise, the proper protocol is to shake hands.
Many Americans, when they are in France, enthusiastically kiss everyone in sight. Not so fast! The boundary between who gets a handshake and who gets a kiss can be subtle. The first time it happens, we make eye contact: one person silently says with their eyes: "I think we have reached the stage in our acquaintance where we can now kiss instead of shaking hands, don't you agree?", and the other person silently assents. When there is any risk of ambiguity, the first person will smile and tentatively ask: "On se fait la bise?", but it would be quite embarrassing if the other person said no, so, if there is any doubt, the safe route is to go for a handshake.
I would say that the people who get a kiss are: family, except perhaps for remote extended family when met for the first time; friends; friends of friends, if they are introduced to us by our friends and if the context is not too formal; acquaintances and colleagues, once a casual friendship starts to develop; and all children. I don't make a difference between blood relatives and other relatives, but some people only kiss the relatives who share some of their genes. I don't kiss my pastor, out of residual respect for some remnant of tradition of authority that he symbolizes, but some people do. The older people are, the more hesitant I am to go for a kiss, and the more I wait for their cue. There are people with whom I go both ways, exchanging either a kiss or a handshake, depending on how formal the context is when we meet. No one I know kisses their garagist, supermarket cashier, or children's schoolteachers. But the boundary is subtle and, I think, very much depends on one's social class.
UPDATE: Here's a simple rule: do not kiss anyone whom you would not befriend on Facebook!