When an immersed body is traveling through a fluid, the surrounding fluid interacts with the body through pressure and wall/surface shear stresses. Lift is the resulting force that is in the normal direction of the upstream velocity, while drag is the resulting force parallel to the upstream velocity. Knowing this, the total resultant force can be calculated as the following
$$ F_R = F_D + F_L = \int PdA + \int \tau_w dA $$
Drag properties can vary based on the characteristics of the object being observed. On a perfectly streamlined body, the drag results completely from the viscous shear stress at the surface of the body. This is a low-magnitude force and is known as Friction drag. For an ultimately blunted object, all the drag results from the pressure difference between the front and back of the object. This is a high-magnitude force and is known as Pressure/Form drag. Likewise, if an object is positioned at an angle, both lift and drag forces will be present. The magnitude of these forces depends on the shear stress and pressure.
Typically, an experiment must be performed to determine the distribution of pressure and wall shear stress, as it is challenging to determine analytically. The most common practice is to define dimensionless lift and drag coefficients, and use experiments to calculate them. The Coefficients of Lift and Drag can be defined as the following:
$$ C_D=\frac {D}{(\frac {1}{2})\rho U^2A} $$
$$ C_L=\frac {L}{(\frac {1}{2})\rho U^2A} $$
To reiterate, Friction drag is the drag resulting from viscous shear stresses on an object. Likewise, with a low Reynolds Number (and corresponding dominating viscous forces), streamlines are considerably deflected more at further distances from the streamlined body; the boundary layer thickness is greater. With a higher Reynolds Number and inertial forces dominating, the boundary layer is much closer to the body and closer streamlines are only slightly deflected.
There are many ways to minimize drag on a streamlined body. Primarily, one would keep the flow laminar; this can also be accomplished by smoothening the surface. Another method would be to reduce the length of the surface, in turn shrinking the area that the drag force acts on.
Boundary layer thickness is the distance from the plate at which the velocity of the fluid is approximately the same as the upstream velocity. This value can be solved for using the Prandlt/Blasius Boundary Layer Solution, where x is the distance along the object.
$$ \frac {\delta}{x}=\frac{5}{\sqrt{Re_x}} $$
Pressure drag, also called Form drag, results from normal stresses (pressure) on an object. This form of drag depends heavily on the shape of the object. Considering inviscid flow around a circular cylinder, the pressure will be equal on each side, resulting in no drag in inviscid flow. With viscous flow, as the Reynolds Number increases, the wake region also increases. In the wake region, the pressure is low and approximately constant. This means that when there is laminar flow, there is higher pressure drag. Thus, turbulent flow is better for a blunt object, as there is a smaller pressure difference.
On a blunt body, a few ways drag can be minimized are by maintaining turbulent flow, roughening the surface, or streamlining the body. Similarly, drag can be minimized by delaying the boundary layer separation.
With streamlined bodies, the drag increases with the roughness of the surface, while on blunt bodies, the drag decreases with surface roughness. This causes the boundary layer to become turbulent and form a narrow wake region. This is why golf balls have many small indentions on their surface, as opposed to a smooth finish.