[Imp]

If your sure its not going to fire in the first turn including reaction fire then doing all the movement in that turn is far better. Or move to cover one hex away from where you want to be & move just the one hex to take up position the next turn.
There can be no hard & fast rule tactical situation is the main criteria. Move fast when your sure its safe & slow when its not.
As stated above you want to move as little as possible to maintain accuracy, Tanks with stabilisers mainly applies to MBT can push it a bit if they have to. Modern top end tanks with good stabilisers FC etc can actually move a reasonable amount & still be fairly accurate so battles are more fluid rather than shoot n scoot.