Watch the Chromatics online guitar lesson by Larry Carlton from 335 Improv
There's probably no easier way to add an interesting element into a solo than to employ chromatics in your phrases. By definition you're just moving up or down in half steps, but a well-shaped chromatic line still sounds great. Chromatics also provide an easy approach for transitioning between chords -- just move chromatically from a chord tone within the prevailing chord to a chord tone within the next chord.
That said, you can also make a mess with chromatics unless you know how to apply them artfully and musically. It's important to target your landing notes: if you know that you want to land on, say, the 7th of a chord, you'll want to start your phrase a few half steps above or below.
Similarly, you might think about a chromatic phrase that flows directly into a scale-based phrase. You also want to be thinking far enough ahead so that you don't run out of fingers! It's easy enough to see where chromatics fall along a single string, but for long lines you'll definitely want to be comfortable keeping chromatic consistency as you cross strings.