I try to catch up to people that I see on the road in front of me, do the same route and try to improve times, listen to music and enjoy the scenery, pretend someone is watching and cares how fast I am going... basically just play games in my mind to stay motivated to improve. Then there are times when the wind kicks my a$$ and I return home early, like Monday...
I was doing about 50/50 split between solo rides and group rides.