well, this is one of those generic threads. i need some specifics. is your ride flat or hilly or undulating? decreasing weight (rider) is important for avg speed on hills for example.

i'd say over the years, learning what gear to be in during different parts of the ride is important. weight is important. intervals are crucial, rest is crucial, base miles and learning how to go slow on your slow days and fast on your fast days.
there is no substitute for time in the saddle. your body knows time, not miles. so it is proper to say that after 100 hours in the saddle for the year i am beginning to feel fit and fast.