For me, I once bought some crypto which were very low in price and I thought holding it for long will produce a long term gain but right now it even losing value. Please, how do I research to know which coin to keep for long term?
You need to grasp the trend of the kind of coin that is trending development. In my opinion, the Etherum Classic (ETC), XLM (Stellar), TRON (TRX) is the trend this year, you can see its price on the chart has no ups and downs not allowed. You can take advantage of the opportunity to invest.