Before we explore the progressive stylings of the mighty Mr Petrucci, a quick check on the basic notes available. And remember, we're talking here about the low B string, just in case there is any confusion with the high B.
Here then, is the chromatic scale of the low B:
Now let's get down to business. Here's an exercise based on the Dream Theatre work of John Petrucci:
Everything is based around that low B, with the rest of the riff mainly employing power chords. Note that the guitar is tuned conventionally, with just the added string - B E A D G B E.
Click here to hear how it sounds: JUST A DREAM (MP3)