Warriors on foot move 6 inches (6") in the movement phase. This represents most creatures moving at a run but stopping several times to observe the surrounding landscape for enemies, snap off a few quick shots with their weapons and so on.
Even warriors who are moving in a part of the battlefield where no enemies may be apparent move 6". This is because your troops lack your own god-like knowledge that there is no enemy around.
A player cannot position a model so that it touches an enemy during the move phase – he must wait until the assault phase to do so. Opposing models must be left at least 1" away in the move phase to keep things clear.