Where exactly do you draw the line between liberals and conservatives?

Personally, I find it hard to do so on most social issues because the positions have changed so fast. I mean 10 years ago, it would've been gay marriage but since then a lot of conservatives have (at least outwardly) been accepting gay marriage. Personally, I use the zoning laws since that's one of the biggest departures from capitalism that republicans support in contravention to almost all of their other stated values.