firstly i will say (not that it never happens but), statistically violent crime in nyc is actually increasingly low right now compared to previous years and compared to other large US cities. i am short and in my 20s and generally i always feel really safe alone on the subway until around 12AM-ish, but after then i might uber. besides a few weird or uncomfortable experiences nothing bad has ever happened to me or (afaik) people i know on the subway, both now and when i was taking it growing up
if you’re going out early in the week (Sun-Wed), be aware that less people will be out the later it gets. but on weekends people will be out really late, especially around bars and in the neighborhoods you’d be going to
some notes/tips - you could always look at the specific bar locations and go to one that‘s under a few minutes’ walk to a subway stop. i also would strongly not recommend getting trashed if you‘re new to the subway so you can have a clear head navigating — and be sure you know the difference between “express” and “local”. also citymapper > google/apple maps
but really the #1 thing is just to mind your business - don’t stare, keep your bag on your lap, and just read/look at your phone/listen to music. i usually wear (wired) earbuds on a lower volume when walking and on the subway so i can hear things but it’s obvious i don’t want to chat ! and in the rare instance someone is making you nervous or just being really annoying, at the next stop you can just switch to a different car on the train