yeah trading is unpredictable job if you want to trade first you need to know that which currency is secure and strong and then you should start trading and trading is depend on you if you have good knowledge about trading then you are good trader.
i agree with you , you are right that first you need to know that which currency is good for trading and then you can start trading with that good currency and its true that trading is depend on your skill or luck .
Tips how to choose crypto if you are using coinmarketcap for checking their volume you should use it to check the volume also search for their more info or details about the security before you can invest if you seen that its safe you can invest how much you want..
If you want lower more your risk you can choose the top 20 altcoin in coinmarket cap that live long in top 20..