Standard tuning is the default tuning for all guitars. When you grab one off the walls of a music store, chances are it's tuned to this one. The guitar was built for standard tuning and the string tension as well as length all play an important role. When you study guitar chords and scales, it is usually for guitars in this default tuning. The string layout is as follows: E-A-D-G-B-E
Since music is art, guitarists like to change things up and find new sounds. Jimi Hendrix would take standard tuning and tune all the strings down a half step. The result is a slightly lower tone which can help vocalists who strain to sing a song in standard tuning. Hendrix would tune down to: E-flat, A-flat, D-flat, G-flat, B-flat, E-flat which gave birth to what we now call hendrix tuning and gave his electric guitar the howl it needed.
Depending on your instrument, this tuning usually calls for light gauge strings on acoustic guitar as well as electric. If you play alot of D chords, try and tune the lowest string (E) down to D. Many folks songs benefit from this, due to the anchor that the deeper D string provides. Another less known hack for guitar tuner standard is to tune down a whole-step, which drops the tone down to a deeper place. Such experiments may call for a heavier string gauge to support the string tension and support the deep resonance.
A good exercise is learning guitar chords and memorizing them. Try and move back and forth between these chords with greater speed.Google+