First define for yourself what level is. Some use the refrig while others use counters, floors, pan of water on the stove top, door swing...
ALWAYS level from side to side first.
Put a bubble level on your trailer/5th wheel pin box where it is visible from the drivers seat. Leveling side to side is usually easy as the work is done by the Tow Vehicle and placing board(s) under the low side wheel(s). Pretty simple.
Leveling from front to rear is done with the electric landing gear. We had a bubble level right above the electric controls for the landing gear.
The legs drop equally but you can move the pin in the legs to compensate for terrain variations.