You should always place them on the floor as so nobody will walk into them and they will be "out of the way".
When driving, the forks of a forklift should be as low as practical. This allows for the best stability while the vehicle is moving.
What is a forklift doing on the highway?
Flat on the ground.
floor level
floor level
floor level
floor level
The forks should ALWAYS be low to the ground while in transit, either loaded or empty.
The forks should be 1 foot above ground
Downhill side
Low as possible
Lower forks to flat on ground, remove key, put brake on.