Value + extra speed = happiness
If you don't have the $ for wind tunnel testing and expensive aero wheels, then your best option for improving aerodynamics is to buy a helmet like this one. (I am assuming most people already have a good bike fit.) All the data out there shows that the cheapest way to cut through the wind is to buy an aero helmet. You have many options to choose from these days, but for comfort and extra speed in hot summer triathlons, the Giro Advantage 2 is tough to beat.