Forgive me if this has been covered somewhere in Mudcat's voluminous history - I couldn't find it on a quick word search.

Here's the query - how do you create a variation of the basic tune when playing fiddle, banjo, guitar, or whatever else ?

I can improvise "lead breaks" a bit on banjo and guitar, playing out of the chord pattern, but those breaks aren't quite the same as playing a different, but still recognizable, version of the melody. Is there a standard technique or theory ?

I know that some genres require variation and others don't. Contest fiddlers seem to strive for a slightly different melodic or rhythmic variation each time through. Bluegrass players often don't get more than one instrumental break per song, but, if they do, then they usually play a variation. Old Timey fiddlers and banjo players seem to stick to just one basic melody over and over. I haven't a clue what the tradition is when it comes to Celtic or Cajun, or Jazz, or Blues ???