in my opinion for beginners what you should be able to avoid is not to be influenced by market conditions and you have to be careful when you want to buy coins, understand the color indication of the exchange, when green means it's the right time to sell not to buy, when it's red or collapsed then it's the right time to buy, sometimes beginners are still influenced to buy when it's green.
Isn't being influenced by market conditions a good thing, I mean if what is popular among the people then the hype could translate into a growth. I do understand a little about when to buy and when to sell but for me the thing that I most avoid is putting a lot of money at the start, in my opinion, testing the waters is a good thing for a newbie trader, this can help you get some experience about many things such wins, losses and break evens, and it can also serve as a way for you to decide whether you want to go into deeper waters because trading is an unforgiving thing to do especially for those who jump right in.