Watch the Concepts and Insight online guitar lesson by TrueFire from Play Rock Guitar 9: Advanced Lick Vocabulary
In this section you'll go over some of the concepts you need to have a grasp on in order to be able to pull off the more advanced licks.
TIP! More advanced licks usually have one of two things, if not both that make them more difficult. Speed and number of notes, and harmonic structure.
I find that working on licks helps me isolate these things. If there is a particularly fast section to a lick, break it down into smaller parts and work on those. Make sure that your picking is correct and efficient, make sure your fretting hand fingers stay close to the fingerboard. These little details are usually what make or break a lick.
If the sound of the lick is new or different to your ear, try isolating the notes that are making it sound that way. Then just play those notes over the chord that is being played and listen to what is happening in there. Sometimes if you can just get the "sound" of the lick to sit properly in your ear, it makes the mechanics of actually playing it much easier.