This is a tricky one, and something I've actually spent a lot of time thinking about. The truth is that you can't find one good, all-encompasing definition for either of the terms; but that doesn't mean they are completely without meaning.
"Conservative" has traditionally been used to describe people favoring a strict adherence to, well, tradition. (Not the status quo, or else Roe v Wade would be a lot more popular.) In places like the Middle East, this might mean favoring Islamism; but in the United States, the "tradition" goes back to the Founding Fathers. Since these were a pretty classical liberal bunch, traditionalist conservatism has become tied to (classical) liberal conservatism (sort of like libertarianism without the Heinlein). Conservatism means small government and free markets for liberals, traditional values and societal structures for traditionalists, and adherence to the Constitution and DoI for both. It could also be all of the above for either, and often is. People can come to the same conclusions through many different methods. Conservatives don't even have to be either traditionalists or classical liberals.
"Liberal" is a bit tricker. One thing I've noticed most of them have in common is a disdain for imperfect conditions - war, poverty, etc. Conservatives and others will write these off as necessary evils, as will to a smaller extent many liberals... but through one way or another, there's always a solution of some sort. I'd probably split it up into two main groups: elitist liberals (no derogatory connotations intended) and populist liberals. Elitists tend to view the main cure of the world's problems as via the powerful, coercive force of a large central government. Since unregulated masses can't take care of themselves enough to not have poverty and violence, they see the need for a group of intelligent, logical-minded elites to be smart where most people are stupid, and to make decisions for the masses that the masses, in their view, are incapable of making. Then there's populist liberals, who don't see the government as a place for elites to converge, but rather as an expression of the will of the people. In their view, it is a choice between government control and corporate control, so one might as well go for the one that is popularly elected. This is the more hippie side of liberals, which doesn't so much see an inherent need for bigger government as for an inherent need for people to change their ways. It's my opinion that the extreme of elitist liberalism is socialism, whereas the extreme of populist liberalism is communism.
Note that the above doesn't even begin to scratch the surface on this, and most of it is probably wrong (or worded imperfectly). It's a fascinating subject that frankly deserves more study than it gets.