Watch the Descending Chromatic Approach online guitar lesson by TrueFire from Play Rock Guitar 10: Advanced Soloing Approaches
Descending Chromatic Approach - Concept 21 is a video guitar lesson presented by Shane Theriot and is sourced from Solo Mojo.
Learning longer chromatic licks and lines can be a good way to get this sound under your fingers as well. Here's an example over Abmin7. The best way to learn these longer ideas is to break them down into several sections and learn each section, one at a time.