Below are some of the video lessons available for mandolin and violin.  You can also view all of the video lesson Playlists in one location.  In addition to lessons, I have uploaded dozens of example of tunes and songs on my YouTube Channel.

Mandolin Lesson - Picking Patterns

Shifting into 3rd Position on the Mandolin

Shifting into 4th Position on the Mandolin

3rd & 4th Position Shifting on the Violin