I'm very very new to Luigi's mansion, but I feel as though I'm getting the hang of it. I just can't seem to figure out how to suck up ghosts nearly as fast as some of the speedrunners I'm watching. In the tutorial it says to just hold the control stick away from the ghost, and while that works a little, I find slightly better success holding away from the ghost and moving it side to side slightly. Is this correct? What is the best way?

I'm sure you know, but make sure to play on Hidden Mansion.

I personally play by pulling in the opposite direction, maintaining control but adjusting as to where the ghost may be, and re-pulling the stick every 10 health. Kind of hard to explain through text without showing a controller, but yeah.

Also Sarcrai made a basics of running LM video, I suggest giving it a watch.

Hope this helps <3