Alternate picking is a big part of my guitar playing style. This is really nothing more than playing a sequence of single notes and picking them down-up-down-up, and so on, throughout an entire lick or phrase. I find it particularly challenging to use alternate picking when playing a long, continuous succession of notes at a fast pace. But doing this consistently and flawlessly requires some diligent practice.
The following lick is one that I like to play when I'm practicing because it's a good warm up for alternate picking. It's challenging to play through the entire phrase cleanly, with uniform precision, and without missing any notes or stopping at any point.
The entire phrase consists of an uninterrupted stream of 16th notes. It begins with the index finger on the low E string at the seventh fret, sounding B. The first eight notes are played on the low E and A strings. You then shift your fretting hand up to the next note in the scale. Starting on beat three of bar 1, the index finger shifts up two frets on the A string to the ninth fret, sounding F#, and the same fingering pattern is then repeated on the A and D strings.
This pattern continues three more times, after which the line descends and the pattern changes slightly. If you examine the left-hand fingerings provided below the tablature, you'll see that the index finger initiates all of the downward position shifts.
This lick comprises two major elements of my playing style: the constant succession of alternate-picked over a long melodic line, and the altering of the phrase's shape, which makes the melody more interesting. I was inspired to play this way by guitarists, such as Al Di Meola and Yngwie Malmsteen, that play linear-style diatonic patterns. But there is also a "baroque" flavor to this lick, which no doubt comes from the time I spent studying J. S. Bach's violin sonatas and partitas.