I understand your desire to die, sad that you are this hurt.
From what I've heard, the most effective way is cutting your arm vertically but it is very painful and has low chances of succeeding (statistically seen). This is because survival instinct will hold you back a bit. I have no clue how you should handle the pain.
I would like to advise against this method, it's very unreliable and if you fail, you probably have to go to the hospital.
I would opt for another method, take a look at the resource megathreads