To buy any coin you need to wait for the rollback of its price down, in my experience do not buy a coin when it has already given a good rise, you need to do this wait until the coin rolls down, but this rule does not always work, you always have to make a decision yourself !
the best time to buy is when the market decreases because we can get coins at relatively low prices, but the problem is that if the market conditions go down we are hesitant to buy coins for fear that the value will continue to fall so we need more courage to do that.