Adding one or two particular color tones to a triad can give a relatively more modern feel to your tunes.  Beyond the triad intervals (1-3-5), adding the ninth, especially when the notes are played individually, occurs often in songs written and performed by many singer/songwriters of the last approximately 60 years. This was common among acoustic guitarists from the mid-60's onward.  Listen to the introduction to Simon and Garfunkel's "The Sound of Silence." 

  You can hear this technique by playing the 1-5-9(all eighth notes) and then you can either either move up a full step to the third or you can move down a full step to the root.  This completes two beats.  To finish the measure, you can toggle between two other chord tones.    Again, all the notes have a duration of eighth notes.  

    After you get comfortable with this, try the same concept by adding the 11th interval.