i don’t race/don’t ride chaingangs etc so this is a very untechnical approach, but there’s a few things i think are useful..
get good at climbing hard (get strava..) – i don’t think it’s the best way to get a fast overall speed, but when you do those hills at a more measured pace later, it seems a lot easier to recover if you’re used to being totally shagged at the top.
don’t finish the effort up a hill until you’re back to your target speed (i.e. 20mph) then recover at that
in the same way, don’t let yourself go under that speed on the flat unless you’re into a very strong wind or something.
but basically just go hard all the time is my main advice.