Something I've found helps this is to listen to the song on repeat. It makes it much easier to learn and to remember when you can play the song back in your head and you know what it is supposed to sound like. Listen to it on your commute to work, working out in the gym...wherever. It helps you learn the song even when you are away from your guitar.

Even with songs you are familiar with, you may have to listen with different ears, listening for some of the finer details you may have missed when just listening for enjoyment.