Watch the Chromatic Passing Notes online guitar lesson by Robert Renman from Blues Booster
Chromatic passing notes is something I learned from listening to jazz players. I often approach a chord tone a half-step below or a half-step above, which makes it a bit a jazzier sounding. It's also a good way to tie licks together, or to make a lick longer if needed. You can add a long line of chromatic notes, as long as you resolve the idea on a good chord tone.