Bass notes are the notes on the 6th, 5th and 4th strings. Instead of strumming the complete chord for every beat, try picking the bass note of the chord on the first beat and then strum the first three or four strings of the chord on the 2nd and 3rd beats. Play the following bass note rhythm holding a G chord shape.
The best bass note to pick is the lowest note of the chord that has the same letter name of the chord. This is called the root note.
When playing a G chord, pick the 6th string note (G note).
When playing a C chord, pick the 5th string note (C note).
When playing an Em chord, pick the 6th string note (E note).
When playing an Am chord, pick the 5th string note (A note).
When playing a D7 chord, pick the 4th string note (D note).
Practice this rhythm technique on each chord separately at first, and remember to hold the full chord shape even though you are not playing all the strings.
Play the following chord progression using the bass note rhythm pattern.