The simple rule is "buy at the bottom and sell at the top". But i don't think this applies to all coins, it only applies to solid coins like bitcoin, ethereum and the likes, because they have stood the test of time and would surely find their way back up. But most of these new coins, if you buy at the bottom, the price might still go lower and keep you trapped there. so it is better to wait and see a clear move up before you get on the train to avoid fake outs.
Following the FOMO hype is not wrong, but you have to think before purchasing because if you are trapped, then you will lose. Follow the Fomo that just happened. For example, yesterday, filecoin was accused of being a scam by Justin. Then you have to quickly short 1-2 minutes after the news of the scam accusation out. In essence, you have to understand a good time to buy.