- Never spend more than you afford to lose. It may kill you. This is the main rule.
- Never treat bitcoin as get rich quick scheme. Get ready to wait at least a year before you see gains.
First is standard, and I agree with the first half of the second point, but I've made 8 times my money in less than three months. People could still get rich in the same amount of time now, but then I'd refer back to your first point.
Don't you remember April 2013 ?
I know many people who spent everything at over $200, and after "crash" they dumped it at half price.
I wasn't watching the markets in April. BTC was only a blip in my radar then.