1. Devide your portfolio in at least five cryptocurrencies.
2. Hold your funds and stop trading during crash or ....
3. ... don't hold and look for cryptocurrencies with little movements or ...
4. ... exchange your BTC/Altcoins into USDT during crash and buy them back later.
5. Don't watch your funds during crash. This may prevent panic sell.
6. Analyse cause of crash and search cryptocurrencies, that are not affected (I didn't find any. But maybe you have more luck )
The things the we needed to do every time market crash are already here and I just want to add just be more patient because this can help you to focus more on your goal instead of worrying about the market. Just hold big coins that you believe can survive even if the market crash, and have the capability to bounce back stronger.