Common advice is to keep your currencies safe by placing them into storage. I feel this is risky considering coins have dumped to all time lows within short periods of time.
Store your coins in the place you have full control of private keys, mnemonic seeds is the best.
You can make deposit to exchanges and sell your coins. Don't worry about flash dumps because price will recover later. Of course, I am saying about good coins, not scam ones. With scam coins, whenever their team finish their planned fundraising, they will do scam exit, and price will hardly recover to where it is (all time high, ie.).
The alternative would be to keep them on an exchange and set stop losses, however, this is also risky as exchanges or your account can be compromised.
Stop losses can be used but it can not completely protect you.
Sometimes, stop loss orders get errors (it mostly occur in flash crashes). Do you think of why we have flash crashes? Partially because of stop loss traps and errors.
Sometimes your exchanges make scam exit and you lose your money. Lose it all.
Don't let your stop losses eat all of your money.