no one has mentioned group riding.
sure you can focus on TT discipline, but at your current level, big gains can be made just by doing a weekly fast paced group ride. It has the same effect as motorpaced training, which was also an effective way to add speed. It's mostly depricated (motorpacing) on the street because it is dangerous and much of the same can be done in group doing strong tempo. One of the things you learn in group is how the shift points of your gearing can help keep your speed/momentum going.
You can gain in two months of wkly fast group rides what might take a yr of grinding the miles out on your own.
There are quite a few such rides within not too far a drive from where you are. Check the big shops and local clubs for info on these. A query in SOCal forum might also give some good references. Along the way you'll also develop some good bike skills.