DADGAD tuning for guitar
I've got two previous hubs on DADGAD tuning, which you may find useful. DADGAD is a widely used tuning for guitar, especially useful for playing Irish, Celtic and folk music in general. It usually has a lot of drone notes, or continuous notes, and this gives chords a lot of depth and sustain. If you want to see the effect of using this tuning, two leading exponents are Pierre Bensusan and Lawrence Juber, who uses it in creating arrangements of Beatles tunes.
To change your guitar tuning to DADGAD:
Strings 6 and 1 go down 2 semitones to D, string 2 goes down 2 semitones to A.
That's it - strings 5,4,3 remain the same.
E A D G B E
D A D G A D
Chord pictures info
In the chord pictures you will see several variants on a D chord - as this is the home chord in this tuning, it's good to experiment with some different voicings. The most simple songs use the I IV and V chords - in the key of D these chords would be D, G, and A. You can play hundreds of songs with just these three chords. Adding Em and Bm will cover hundreds more songs. The chord names are a bit approximate, and I wouldn't worry about exact chord naming. Rather, think of this tuning as a kind of musical playground where you can shift chords up and down the neck and discover new things.
If you are into songwriting, this can get some great results - Joni Mitchell is the pre-eminent example of writing songs from the standpoint of different tunings.
More chord pictures
Try the D/Fsharp chord in line 4. The next chord pictures show part of a harmonised scale of two-note chords going up the neck, ending in D. The D major scale is shown next, again it's going up the neck. You can combine these notes to play chord melody style pieces, where the melody line and chords are used together.
The D major scale can be described in fret numbers, all on the 4th string (D):
0 2 4 5 7 9 11 12
The E7 is a non-diatonic chord in this key. The next chord is an Am7, although the normal tuning shape would be an A7.
This 8 - note scale is the basis of all Western music.
Try using harmonics at the following frets: 12, 7, 5. It's a nice effect in open tunings.