Try the following rhythm variations and make up your own. The bass note one the first beat of the var can be substituted for a normal down strum. Apply these rhythms to any chord progression you like. All these suggested variations are in * time but the same principle can be applied to ^ time. Also note that in all these rhythms your right hand moves up and down in a continuous motion. These rhythm patterns can sound "off the beat". This is called syncopation.
Rhythm Pattern
Rhythm Pattern
Rhythm Pattern
Rhythm Pattern
Rhythm Pattern
Rhythm Pattern