One of the best way is to protect your private key never give it out to any one even if it's your mentor that is very important
This is for new guys like me
If you're using a wallet based in private key (Myetherwallet, Metamask etc) the safest is to archive with password the file containing your private key and, if course, not to holding it on online platforms (e-mail, google drive etc).
Personally, I'm a big fan of cold wallets. I bought a Ledger Nano S, it has no private key, funds cannot be stolen from here and this is definitely the safest solution existing today. (It costs ~100$, but it worths every single penny )