something i like to do:
if an opponent fires at you from kinda far away, put trees (etc) between you two and advance!
for instance, move to the left/right until there is a tree between you two, then move up to it. move left/right until there is another tree between you two and move up. repeat as necessary.
obviously this doesnt work if there is more than one opponent you have to worry about. you'd get flanked fast!