the best trick I learned is to stand near the door you entered so all the ghosts will spawn in front of you, then flash them once they bunch up (varies on room type, but works well for the first floor). once you suction them, move backwards, and if there's a pillar or table, use it to stop yourself from getting dragged. you can also flash enemies through walls and tables, and suction them through walls and tables as well. ghosts also get suck on pillars and objects, so if you stand behind one, they become an easy target.