If you see the market going down, stop loss before it's too late. You may lose 5-10% of the capital but when the market goes down you can buy more btc, eth when you hold btc, eth, altcoin.
At the same time, do you know that the market can revert to profit and give you some percentage as soon as you exit. Sometimes, some losses turn to profit within seconds as far as trade is concern.
I think that the richest people in the cryptocurrency are those who invest and do not cash until and unless their profit is the maximum. They normally invest when the market value of investment is the least. So better follow this ideology and stay for as long as possible. Do not cash out even when the market is a bit better. Cash a part of your coins when you can get the maximum output.