You can never be 100% safe using a centralized exchange. By definition, your coins at some point have to be under their control, and therefore you are exposed to risks of hacks, exit scams, shutting down, freezing your accounts, and all the rest of it. You can lessen this risk by only sending coins to an exchange when you are ready to trade, and withdrawing them immediately once the trade is complete. You would also do well to avoid new and smaller exchanges, and stick to the big players such as Binance. Although you can still lose your coins with big exchanges (Mt Gox for example), the number of small exchanges which are hacked or scam their users is much higher.

The only way to avoid the risks associated with centralized exchanges is to trade peer to peer. Doing so, however, exposes you to the risk of trading with a malicious third party. There are platforms such as Paxful and Bisq which will link you with a third party and act as the escrow to try to ensure a smooth deal.