to best protect your work with MyEtherWallet you can use it :
a) Locally, that is, on your computer, without entering keys and passwords online;
b) as a cold wallet, on a computer that is not connected to the network at all.
The second option is most preferable because it provides the highest level of security. Of course, the use of a cold or local wallet does not eliminate the need to install anti-viruses, and maintain a neat lifestyle on the Internet as a whole.
Third option to protect your assets with myetherwallet is buy a hardware wallet, such as ledger or trezor, that pendrive is our private key and nobody knew that, hardware wallet have a high level security to protect our assets, just remember don't use private key to login myetherwallet, it's not a recommend way to access your wallet because entering your private key on a website is dangerous