Ga / Floor advice

I plan on getting Ga tickets this time around for Oasis. I'm fairly new to concerts and never done GA at a stadium before.

What are some tips and tricks for getting a decent spot?

How do you stay somewhat comfortable?

If you do need to leave your spot for any reason, what are the chances of getting it back?

Just in general what are some good pointers?
I don't plan on getting barrier or anything but would like to have a spot somewhere in the middle towards the front.