Eddie van Halen is, maybe, the most influential guitar player since Jimi Hendrix. Playing solos that are perfectly built to serve the song, Van Halen's techniques had a major impact over all rock guitarists. We'll take a look at some of them:
Van Halen often uses fast scale patterns, played three notes per string (see 3 by 3 scales). An example from Jump:

And another one from Girl Gone Bad:

Repetitive intervals are another Van Halen trademark. From Finish What You Started:

Van Halen often uses double-stops. The riff from Hot For Teacher:

Thirds from The Full Bug:

Tremolo picking is one of the most preferd Van Halen techniques. Here is a short example of thirds played with tremolo picking from Girl Gone Bad:

Van Halen chooses carefully the sound of every note. Noone prior to Van Halen used the whammy bar and the pinched harmonics as powerful and frequently. From House Of Pain:

Van Halen's use of arpeggios is complex and melodic. An example from Cathedral:

There are also fast runs that are backed by free strings, like this one from Spanish Fly:

And the same technique in Eruption:

Again from Spanish Fly, the next lick where Van Halen uses tapping and free strings:

And a more extended piece, the riff of Source Of Infection:

Eruption was the piece of music where Van Halen and his tapping technique emerged:

Van Halen also experienced with two fingers tapping. The right hand in the next example from Judgement Day is marked with T:
