1. Spend less than you make and invest the difference in a low cost broad market index.

2. Work to increase the difference.

I don't follow buy low sell high. Instead I buy regularly and don't sell.

The term for that is dollar cost averaging and it's the idea behind the rule of "don't try and time the market".

only invest what you are willing to lose.

It’s not really worth it to save money if you have credit card debt, cuz interest rates are brutal. Pay off your credit card debt first!

Low fee index fund or bust.

buy low sell high?

Time in the market > timing the market

Investing is a long term game.

Don't gamble with the rent money.

Pay off all your debts first.

Don't put all your eggs in one basket.

Use a discount broker like Vanguard or Schwab.

(all tried and true platitudes)

Personal finance is covered well by the others but for investment: buy and hold.

As in: time in the market beats timing the market. "Buy low" doesn't work if you don't have market shifting money or insider information most of the time. Don't try.

The same is true for cherry picking: people hunting the next big thing spend a significant portion of their money doing so - and never rarely do the math if it's worth it.

Buy low, sell high is applicable to trading securities which is only a minor part overall of personal finance.

Personal finance in its whole is a system for managing the flow of one’s money in an optimized way which both minimizes losses to taxes and interest while maximizing ROI.

A great starting resource is the Bogleheads wiki: https://www.bogleheads.org/wiki/Getting_started

They provide general flows to managing personal finances.