3.
As a blaster you will often need to run away,
don't wait for someone to shout 'run' or for your health to
turn red, start running when the mobs turn to shoot at you.
Never just run in a straight line and rely on distance, always
either hide behind something very big (e.g. a building) or
run round a corner if indoors.
After you've lost line of sight stay close to the corner but
safely tucked away and use some camera angles and zooming out
to watch the mobs chasing you, once someone else has picked up
aggro from them you can get back in the fight.
Sometimes you will have powerful defenders backing you up
and you won't want to run at all, force fields and fortitude
are both good signs that this is the case.