The best time to sell off your crypto investment is either when the market value of the crypto coin you invested goes a bit higher than the initial value you invested or when the value drops to avoid you from losting a greater portion of your initial investment.
Yes, selling coins must look at the market situation. And don't rush to sell coins because the price of coins will definitely rise again. I think trading is very fun because now the market is in very good condition to sell coins.
That's a good decision to consider a market trend before trading. And also you may have some predetermined profit price of token to sell it. Otherwise you will loose a good moment waiting for the best one.
I agree it's best to always sell, of course, when there is a pump. But keep in mind that coins that go high tends to drop also. But it's just for a short period of time. So I would suggest that you sell on top and try to buy back coins from where first bought it. There is a big chance the coin will go back there. For losing coins, better cut of the investment as soon as you see the trend going down.