Grace notes can be thought of as a great tool to have in your DADGAD guitar tool belt. This is true for both composition as well as just daily playing in DADGAD. Grace notes are part of a category in fingerstyle guitar called ornamentation. Basically I like to look at ornamentation as putting ornaments on a Christmas tree. You can certainly just keep your Christmas tree bland without adding anything to it and it would be fine. But adding ornaments to the tree really makes it come alive with beauty and interest. I see guitar ornamentation in the same way. You can play a song without ornamentation in DADGAD and it will be fine and even move audience. But adding ornamentation can add both beauty and interest just like our Christmas tree example.
Basically a grace note is a very quick hammer on note that happens so fast you might miss it other then the fact the ear and mind are so fast they do in fact pick it up! Kind of magical how it works I think. As noted in this website I am currently writing a new song book for DADGAD Guitar Hymns with arrangements I have created over the past years. So here is an example of a grace note in my Amazing Grace arrangement. You can see that the note is very small and proceeds the primary note. It is good to kind of practice grace notes in your playing by for example playing an E note on the first DADGAD D string and then a very very fast hammer on to the F note on same string. With practice you can kind of hit the grace note very nicely as a very fast and passing note and it will add really a lot of nice interest to your song. It is important to play that grace note as kind of a 32nd note really fast and then land on the primary note and let it ring as a normal quarter or whatever note it is.
I will try and add some sound examples soon of this. I think you will have fun with grace notes and they will add a lot to your song!