1. Invest in Bitcoin with your spare money:
2. Invest what you are able to lose;
I think these stay. Although risk-tolerance is different from one person to another, if you want to be safe and not lose sleep whatever happens to your investment, invest only an amount that is not intended for something else and not big enough to give you stress when you lose.
Whatever Bitcoin has proven in the past decade, it is never a guarantee of what is to come. It is never even a guarantee that Bitcoin will still be here 10 years from now. That Bitcoin's price grew thousands of fold in the past decade doesn't mean it will x5 in the next decade.
To those people who put their retirement money into bitcoin, I hope they didn't go all-in. To those people who have all their savings in Bitcoin, you're probably doing it wrong.
3. DYOR (Do your own research):
This advice should be for altcoin investors. If I may ask, what kind of research is one, especially a newbie expected to make in bitcoin. Are they researching the road map of bitcoin or are they researching the developers behind it? The right thing is to know when to buy. Simply buy low and sell high.
This classic advice won't age. It will always be relevant not only in terms of investment but also in terms of everything else in life. You should do your own research in choosing which to invest, who to marry, what kind of house to build, what brand of car to buy, what supplement to drink, and so on and so forth.
In terms of Bitcoin, you shouldn't stop researching. News affect it. Government policies affect it. Economics affect it. A hardware wallet suddenly introduces cloud backup and KYC. A mixing service keeps sensitive information.
You say buy low sell high, but how to do it without research?