How do you bicycle the most efficiently on a road bicycle?
The first answer is: you bike most efficiently inside a peloton (where air resistance is lowest)
The second answer (in a GCN video of a sprinter): you do a lot or close to no effort in order to stay at a certain speed (stay on the average). Any increase of speed means you lose a lot more to aerodynamic effect. This usually means you give everything on uphills and recover on downhills (assuming sprint-type uphills and downhills, i.e. 5% or so).

The general idea is that the average speed is much more affected by slow segments than by fast segments, so you want to increase as much as possible the speed on the slow segments, even with a significant decrease on the fast segments (if you drive 99km at 99 km/h and 1km at 1 km/h, the average speed over those 100km is about 50 km/h - one percent of the length at a very low speed just about halves the average on the rest)