This is all about your experience. You'll know when to sell soon, take your time, watch the market's fluctuations and be patient. Also, learn from your mistakes. Check out some cryptocurrency channels on YT like for example SideChain Podcast. You can also use one of the useful tools for beginners, for example CoinDeal has a feature called the Galaxy Score and it could helop you to decide when is the right time to sell or buy and which coin, check out:https://coindeal.com/support/article/galaxy-score