Always use good reputed exchangers (bittrex , poloniex , binance) with good volume(24hours trade volume).
Do not use the email of your social media accounts for exchangers login. I would open a separate email created for this purpose . Use a strong password for exchangers and email (dont use same password ) .
Please verify KYC (know your customer) before doing any trade/exchange.
Enable 2FA(2 factor authentication) for both email and exchanger login .
Never click any verification link sent to your email unless its requested by you .
Periodically check the login history (check the ip from history ).
Always double check the address bar for correct url . I would bookmark them and use from there .
Never ever share your credentials (not even the email address) with anybody.