I know a lot of people are having difficulty finding the sweet spot, I'll try and explain with what I've learned.
First of all if you are using your fingers, and you try to press against the artery from the side, the artery tends to feel like it's rolling forward behind the windpipe into that space, and it'll just hurt the more you press. From behind the windpipe you need to press in the direction that points through the very center of your neck. This will keep the artery flat against the underlying tissue and allow you to apply firm pressure without being painful and prevent it from rolling out of the way. Standing for me is easiest, but I worry about falling if I make myself black out, so sitting may be the best for finger practice. Trying to use fingers while laying down doesn't seem to work at all for me, I'm guessing because the neck is out of alignment in some odd way.
The small filled bags (Cornhole bags) combined with the ratchet or duck tape pull almost perfectly towards the center of your neck because of their circular inward force, so you shouldn't encounter this problem. If you feel excessive pressure then it's too far back, if you feel choked it's too far forward.
My "sweet spot" is two to three fingerwidths down from the bottom of my jaw, near the top of the neck. Whatever bags you use should be either as far up as they can go up or very close to it. Same with the strap / duct tape. I think a lot of people are placing them both too far down on the neck, try higher up if you aren't getting any good results.
Like many previous posters stated, try different areas for 10-15 seconds and feel the results. You'll know very quickly if you're doing it correctly or not. Don't be discouraged, finding the correct area shouldn't take too long if you're patient. Remember you need very little actual pressure once you have the right spot, but the location and direction of force are key! You should feel light headed very quickly and black out before you feel any excessive pain or pressure.
