I would pick one person at random, follow them around for the whole day, and whisper things to them. I would also throw crap around and really freak them out.
Pull a lot of pranks and scare my sister :D, she's terrified of those 映画 like paranormal activity and the conjuring, i'd probably get in huge trouble but whatever
Well I would fly to the UK an hug my three favourite youtubers that live there (Danisnotonfire , Amazingphil, PewDiePie) then fly back ホーム hopefully before the 次 日 when I wouldn't be invisible