Watch the SECTION 2: Open E Tuning online guitar lesson by Andy Aledort from Slide Guitar Power
In my opinion, the best way to get started with slide guitar is to use an open tuning, and one of the most popular open slide tunings is open E (low to high: E B E G# B E). In this tuning, the sixth, second and first strings - E, B and E, respectively - are tuned normally, while the A and D strings are tuned up one whole setp to B and E, and the G string is tuned up one half step to G#. With the strings tuned in this manner, an open E major chord is sounded by strumming across all of the open strings. Likewise, laying a fretting finger across all of the strings at a given fret will yield a major chord: in open E tuning, fretting all of the strings at the third fret will sound a G major chord; fretting all of the strings at the fifth fret will sound an A major chord; fretting all of the strings at the seventh fret will sound a B major chord, etc. The slide can then be used to fret across multiple strings at a time to sound smaller major chord voicings along with single-note riffs as used for solos and melodies. Slide masters such as Elmore James, Duane Allman and Ry Cooder have all exploited the open E tuning (and its common variants) to great effect in their classic, essential recordings.