Watch the Using Common Tones online guitar lesson by Brad Carlton from Guitar Lab: The Imaj7 VIIm7 Progression
In this video, I'll demonstrate the principle of using common tones when playing over two different chords. This is a very effective musical technique which allows you to sustain a note over the chord change instead of feeling obligated to play a different note. This principle can also be utilized to provide forward momentum in your melody even when the note you sustain is not a strong chord tone over your destination chord. You simply resolve the weaker note, which was your common tone to a strong chord tone. And remember, you won't always target chord tones but you want to have the skill set to do so.