I normally use headphones to make it easier to pick out the subtle stuff. If I cannot figure it out, I surf for (gasp) tabs that might get me closer. Generally I find most free tabs to be pretty inaccurate but they are a decent start. I will play small sections of the song, maybe two measures, over and over and over until I get it and then try to connect them as I learn more.
If it is possible, I will buy a book of real honest-to-goodness sheet music. I have a good one with Clapton stuff, one with some Police stuff and another with a bunch-o-Motown. These will often have tabs underneath the standard notation. That is the best way IMHO but not all music is available in this flavor.