Welcome! You will find that questions get answered pretty quickly here.
Good call on the tire replacement, that was going to be my second suggestion.
Because you said this was your first bike, my first suggestion would be to enroll in a MSF Basic Rider Course if you haven't already. That will make sure you get started riding with proper technique.
I would also suggest that you purchase an entire set of gear - helmet, jacket, pants, boots, gloves - and wear all of it all the time. You may want mesh gear in your area, but gear is very important no matter what the temp.
Check out CL for used gear. I've picked up some quality used gear for cheap over the years.
This is a link to the technical section with a ton of good info -
https://faq.ninja250.org/wiki/Ninja250_Howto
Best of luck. Have fun with your new sport!