A simple way to render a basic I,IV,V tune and "jazz" it up....is:
1. Play the first phrase....
2. Use the 1/2 tones of the highest note of the chord
3. Play a descending or ascending four notes
4. Move on to the second phrase...and so forth
Explanation:
1. A phrase is where the tune pauses
ie....(1)Row, Row, Row your boat....(4half tones lower)... (2) Gently down the stream (4half tones higher)
ie... Won't you come Bill Baily (4half tones descending)Won't you come home (4half tones descending)
Mechanics and your ear tell you wether to go up or down.
2. The 1/2 tones are the frets on Guit/Banj... they are the blackkeys (key of C) on the piano/org...they are the slide bar on a fancy harmonica... by using 1/2 notes you are playing a chromatic scale.
The chromatics can begin as quarter notes....and then later you can experiment with eighths and dotted quarters...doubled noted and other embellishments....
Start with a simple tune...and play around with it....you'll be surprised...and most of all....