Here’s something fun you can do on the fiddle. Alternate between a constant note and other changing notes, always alternating back to open D. This is called a “pedal pattern”.
Here’s a basic pedal pattern:
Here’s a variation in which we move down the scale notes and then jump back up:
You can also go from the A string to the D string:
You can make up many different patterns. The sky’s the limit!
You can add rhythms like hoedown or triplets.
That’s just the tip of the iceberg for creative things you can do with pedal patterns.