How do I know when to sell my crypto coins when the market rising and dropping rates are not stable?
Selling of crypto assets now is not really the very best idea, except you are aiming on acquiring more Bitcoin ahead of the on going and up coming market bull run.
If I am to answer your question directly, I will say, the right time to sell is when you have a certain amount you wish to get from the market. When that price is attained, then that is the right time to sell. The crypto market is a volatile industry, where there is price manipulation of all coins by Whales. This price manipulations can be in favor of you or could be disastrous at the end.
Another thing that you can look out for before selling your coins, is if the project is stagnant in price and does not have much trading pairs, no development of project or poor project team members and if it is facing delisting from it's top exchanges where is listed and other different exchanges. When any coin starts facing these, then that coin or project is about to fail or fold up. The reason for these could vary from one thing to another, and if the project team are not sincere enough, they just disappear into thin air without trace.
Continuous development in the crypto community is what keeps a coin going, and a coin that is rising or yielding profit is kept that more profits can be acquired.