I would practice more with strangulation, it is reliable, effective and wicked fast if done properly, plastic bag would be more likely to cause panic usually associated with being unable to breathe, with strangulation you just kinda black out after 5 seconds or sometimes even less. Once you get it right you will know instantly. You will lose your vision, and your whole body will go tingly and limp with sparkly pins and needles, you will also feel very light, after those physical effects you will start to hallunicate and "see stars" so to speak. All of those things will happen nearly right away, if you dont feel any of those things the bloodflow was not properly cut off. As far as users on this site im probably one of the biggest "fans" of strangulation on here so take what I say with a grain of salt, I'm biased because I truly think it might be the most accessible and even enjoyable ctb method, I would reccomend it above all other methods personally. I've messed with it tons, and i've even gone into the characteristic death throws and seizing before and none of it is painful or distressing. you just kind of feel high or something+ total lack of awareness. It's 100% my choice for when I feel like trying again. You just REALLY have to make sure you're alone so you don't get taken out of your ligature, thats where I screwed up previously.