Vitality improves your chances of surviving a wound by decreasing the possibility of bleeding and instant death through critical damage of a body part.
Vitality can easily be raised by running through a fire to take damage. Be careful not to stay too long in the fire because of the high damage it causes. You can use Regenerative stimulant injector eTG-change and Propital to heal yourself
A safer option to raise vitality is to obtain a heavy bleed and use Propital to heal yourself without fixing the heavy bleed.You can also use barbed wire with it's lower damage output and combine these two options.