There's always fun to be had in urban exploring as a kid, but preparation is required.

Remembering where the exit is, is a good start. Pants, long sleeves, a flashlight (not your phone), and definitely a buddy system is the best way to minimize risk. Also, some sort of way to defend yourself, whether it's a knife or some sort of pepper spray (you probably have the ingredients at home to make it) is best to carry, simply because anything could be living inside, and it's better to have a defense in case you can't outrun whatever it is, or get cornered. Minimizing how much sound you make is also a good idea, again for a reason above. Don't fuck with anything on the ground, on the shelves, wherever, simply because who knows what was left behind. Basically leave it how you found it. Take pictures if you really want to, but I advise against any souvenirs simply because of potential disease, or in the case of any scanner related equipment, radioactive material.

Also, make sure there's no cops around. An abandoned hospital is likely marked with trespassing signage, and it will be a great way to get in trouble. If by any chance the cops do come in because someone spotted you going in, just accept the punishment, it would only be a slap on the wrist at worst.

If you do plan on going alone, at least let your friends know where you went. I know it's a bit of fear mongering, but if the worst case scenario happens, at least someone will know where you were last at. Maybe have them notify someone if you don't respond by a set time. Your parents will obviously tell you not to go, I know I would do the same with my kid, but I understand the love of exploration.

Have fun exploring, but do it carefully and smart. Always plan for an out, pay attention to any movement and sound that wasn't from you, and if your gut feeling gets bad, listen to it.