I kind of start out with a very simple explanation, and am willing to expand on it if the person actually seems interested. The one on my leg, in Elvish, is the one I get asked about the most, since it's most inscrutable (and also highly visible). In short, I say, "It says, 'Not all those who wander are lost.'" If they seem satisfied, I drop it. If they ask what language, I tell them, and then offer more if they want it. I guess it's just part of having tattoos, having to explain them. =)