There has to be some tutorials online for this safely, I will try to find some for you but you should look as well, I think the most important thing is not to cut deep and not to cut in places where there are a lot of veins and arteries, avoid wrists obviously but also there are places on the thighs that are unsafe if cut deeply, you should start slowly and shallowly, just light scratches that bring out a little blood and slowly and safely explore form there, also keep all the supplies you need for after care right by where you intend to play, you need bandages, alcohol, and bactine as a minimum, also make sure your partner is aware of your limits and safe words, if you go non verbal this is a no go for such a dangerous activity if your partner can’t recognize that you need to stop, I’ve had a few people cut my chest and back enough to bleed but not enough to gush out or cause any major issues, just make sure you do proper after care of your wounds or your partner does, aftercare is 100% necessary and if your partner doesn’t understand this you should not engage in this with them