i have my own method which I don't want to go into detail cus most of it is second nature to me. Half of it is gut feeling. One part of it is, paying attention to how fast the transactions (and paying to supply/demand amounts) are coming in to tell how fast and much the price will move in a given period of time. Once it slows down it most likely will not go much lower for the time being. Even if it does, you don't lose much by holding and waiting for it to come back up. Alternatively, if you think you got in at a bad price, it doesn't hurt to sell it since the fees are so low compared to stock trading and the good thing is that there aren't prohibitive day-trading regulations and fees with crypto like there are with stocks.
i can also tell the difference between a real price drop due to lack of interest and a flash-crash /panic sell