To be able to improvise well over a chord progression, it is essential to know the notes contained in each of the chords and be able to play them at will. A good way to develop this ability is to memorize the scale tone chords in the key you are working on and then practice various combinations of them.
Here are the seven scale tone triads in C major played as arpeggios. The ascending pattern in bars 1 to 4 begins on the root of each new chord, while the descending pattern in bars 5 to 8 begins on the 5th of each new chord.