Should I be taking advantage of flats and downhills by pushing it, since I'll be inevitably be creeping up hills? Or should I take advantage of them by taking it relatively easy and saving my energy for the hills?
In general, a cyclist's average speed for a mix of terrain will benefit if the most of his/her effort is applied during climbing. And again, in general, overcoming the steepest uphill parts of the course with the most effort is
theoretically the most beneficial. However, in practice the human body is not capable of uniformly monitoring itself to determine a perfect application of power for a set varying loads. (this means even using a power meter isn't always helpful)
I never really have any clue how I should pace myself for Max efficiency.
A good start would be to realize that when you mention "Max efficiency" you'd better decide whether you are talking about your body or your bicycle ride.
Two of the most important aspects of any time-trial expert's abilities is the personal talent of knowing when his/her body will benefit from standing - and inversely when it it is better to simply "freewheel" down a mountain.
You can draw some expertise from runners' histories - they know they have an optimal sustainable pace - they train hard and easy to find it. And them they measure that pace across the course distance that confronts them. in cycling -this seems incredible in the face of multi-gear bikes and the ability to "coast." Yet you still end the the ride with an average "overall effort" (or Heart rate avg)