Move obliquely. In an unpredictable manner. An oblique move gives two elements to deal with when moving. Jerkly random moves prevent precise aiming.
One of my instructors, Silver Star winner, had the ability to move across the battle field with out getting hit.
He never moved in a predictiable manner, never broke cover for more than 1 second and his moves were allways at a diagonal.
If memory serves, it takes a trained infantryman 1.5 seconds to acquire, aim and hit a target. This is the reason for the 1 second exposure.
Finally, a definition of trees vs bushes. Per a Special Forces Captain when asked how many types of trees existed. "There are two types of trees. Biguns and littleuns. Biguns you can hide behind and they will stop a bullet. Littleuns you can hide behind but they won't stop a bullet.
Cover is the same.