There is not a moment where is better to take profits.
When you start investing you should have a strategy with a well-studied asset allocation. So with periodic rebalancing you will buy when the price goes down and sell when the price goes up, as the allocation will be unbalanced by the market performances of your coins.
Obviously it is an extreme simplification, but I advise you to start studying how to build a well-organized portfolio, otherwise it cannot be considered investment, but trading/gambling.
Its always trading. It always does sound a very newbie question and probably don't know terms even. Oversimplification would be more like buy low sell high. But since he is asking when to sell, it means he likes to identify when to know he is not going to lose potential profit after selling.
But this also depend on which timeframe he is selling or whether he is a short or long term investor, either I woukd still suggest using RSI for his trading.