ok, to practice getting better at timing/chord changes/rhythm, I have been only going from C to Em....then I tried adding in D7....but I just can't grasp that yet. Soooo..I am looking for another chord that is easy to fret going from Em that sounds good with the C and Em.

Can anyone suggest another chord?

I was doing: C - Em - D7 - G7
sounds really nice but i just cant get good timing or rhythm on the changing.