The cornerstone of any performance or mission analysis calculation, will be the airplane's drag polar. For the purposes of this presentation, we will be looking at a classical drag polar representation. There are modified versions of the drag polar in use, but for our purposes, the classical representation should serve just fine.
Similarly, the parasitic drag will be a function of the airplane's wetted area, the coefficient of friction (book keeping the effects of rivets and similar protrusions), and the Mach number. Particularly in transonic and supersonic flight, the parasitic drag can be expected to rise significantly due to wave drag.
Finally, in addition to being affected by fuselage integration, wing cross section, and similar effects, the aerodynamic efficiency will also be a function of the airplane's Mach number, and aerodynamic loading (or g-loading).
The mission analysis in turn is calculated by breaking the mission down into small segments, which can then be analyzed for fuel burn. Effectively, the airplane is analytically "flown" through the mission. In its most simple form this principal can be expressed by the Breguet range equation - which also provides insight into what these equations can tell us.
Part of the real beauty of the relationships described here, is that they allow us to draw comparisons and conclusions from different design trades without necessarily exercising a detailed mission calculation. Consider for example the Boeing 777X currently under development as a more fuel efficient, longer range development of the original 777 design. The 777X is expected to increase the wingspan of the airplane from the 212-ft 7-in found on the 777-200LR, to 235-ft 6-in for the 777-8X - a 10.8% increase.
From the drag polar, the maximum lift-to-drag can be calculated from the relationship shown below. Note that the lift-to-drag ratio is related to the square root of the wing aspect ratio, which in turn is related to the wingspan squared. Assuming a constant wing area, therefore, we would conclude that the 777X should offer a 10.8% increase in range over existing 777 models - just by virtue of the increased aspect ratio alone.