Trading in crypto is too risky than other market like stocks and forex, trading in crypto requires more and more of time and research effort since we can trade anytime it is prone to high change in dump and pump. We might miss some chances if we don't look at the graph or visit our exchanges even in one day.
Not only stocks, everywhere it is impossible for us to predict them in the market. Some times it is impossible for us to sell them because the price of a coin may increase even higher value and sometimes we might miss the boat like what was happened in 2017. So it is always good to set your goals before purchasing and selling your coins.
Depends on what you have and what you need to do with what you have. You should day trade if you have for example Eth and you are happy with the rise though there has been no pretty good rise in ETH lately. Any coin that can give you profit could be cashed if you need the money but if not, HODL till the market is fully bullish would be the best option for you because you would get high value addition.