When it is falling, a lot of people will ask you to buy or to hold, but you should look for the reasons why the price is falling, if its caused by usual correction then holding or buying is already correct, but if you found something suspicious, like the coin developer want to scammed people or there are weakness in the coin, then you should sell, investing in alt coin need patience and need a strong mind
When market is falling just hold your coin a little bit longer then observe a few months. Because Crypto is always changing maybe this week is going down but next week or maybe next months is coming up big. So the tactics is be calm and focus in investment sometimes its better to buy times like this while coin is cheaper,so that when selling it back in high market time you profit more.