How do you press hard? well idk how to answer that one tbh, you just use pressure with your fingers (try the "U" shape, and press inwards, as if you were trying to reach the back of your neck), not a lot since only 3-5kg is needed to close the arteries. And, you know when you got it when you start to feel dizzy and your vision blurs (aroun 10-20 seconds, if nothing happens stop and start again). Push where you feel the strongest pulse in your neck, you'll get it eventually, takes some practice, don't give up.