Use passing tones in the bass to keep the harmony interesting.

You want the bass to move, especially when you are changing chords.  Try to track where the chords are going and keep passing tones flowing between the chords in the space between measures.  You want it to flow nicely.

 If you know you are building to a C from G, try putting a G/B between the G and C.  This will help it keep flowing nicely.  You have to keep inversions in mind not just in the right hand, but in the relationship between your left hand and your right hand to make the bass flow nicely.