Quote from the NFPA Fire Protection Handbook, 18th edition, 6-352
"The more GENTLY the foam is applied,
the more rapid the extinguishment and the lower the total amount of agent required."

Conducted by targeting the foam stream before the flame/fuel front and using the stream to push a "wave" of foam over the area by sweeping the stream left to right.
On a spill fire, you will only be able to "push the wave" so far and another technique may have to be employed.

"Lobbing" or "Rain Down" may be required when objects block "rolling" techniques or when debris clutters an area.
The technique still requires gentle application.
The area is "painted" progressively toward the fire.

Banking uses deflection from another object such as a tank or wall to allow foam to flow downward and spread out over the intended area. Can be useful when storage tanks have a containment area. Banking/lobbing may be used to insulate other surfaces.

"Rolling" or "Wave" 

"Lobbing" or "Rain Down" 

"Banking" 

A combination of all three is likely for most incidents