Darth Lefty 

If you can scout a route with less stopping and less climbing that is a good bet. It doesn’t just pause your time, it exhausts you.

Also good if everything on your bike is working properly. Drag from seals and grease is baked in, but drag from badly adjusted or filthy bearings can slow you down while it’s also chewing up your bike.

Tires can make a difference but it’s a trade off. Faster lighter tires have less armor. Light tires are just nicer to ride on. That’s why some of us go tubeless, but it’s not a panacea either. Slick tread is faster.

If you are going fast enough to worry about aerodynamic efficiency then it’s easy to understand. Get in the drops. Smooth round shapes, which means tight fitting clothes, nothing flapping, no luggage outside your front silhouette