These tips are all focused on the second part (not losing it):
Don't give out your private key
Don't lose your private key
Triple-check addresses before sending any money, and use copy&paste or QR codes wherever possible rather than typing it out (doublecheck the currency too, as there's lots of similarly named coins and some share wallet address formats)
Don't delete old wallets/addresses you're not using anymore in case someone you gave the address to a while back sends money unexpectedly
Enable 2-factor authentication on any exchanges/etc. you use
Keep any bitcoin you're not planning on using imminently in a paper wallet (don't keep it stored on exchanges as they're targets for hackers.. MtGox & Coincheck both had ~$500mil stolen)
Generate your paper wallet address using a computer that isn't hooked up to the internet.. keep wallet backups in a safety deposit box or something
Don't fall for any of the scams.. there's an absolute shitload of Ponzi schemes, etc. which claim to give you a large return in a short amount of time.. they're essentially all scams.
I'd keep PayPal as well since there's a lot of people/companies/etc. who still don't use/accept BTC.
Good luck! :money: :money: :money:
Thanks for your feedback! I'll try to keep all of these in mind so I don't lose any money.