The link above for bogleheads changed my investment life forever.
Their basic strategy is simple:
1. Time in the market is more important than market timing (Which is impossible anyway and stressful). Invest on a schedule and don’t worry about daily / weekly swings.
2. Balance your risk comfort level between equities (market funds recommended) and fixed income (bond funds, treasury funds and the like). Pick a percentage for equities and stay with it. If the market goes up, sell equities into fixed income. If the market goes down, buy equities from fixed income.
It is so simple to follow. I am retired and so I am only 30% equities. Others my have a higher risk acceptance and hold a higher percentage equities. Process still works the same.
I found this information out later in life. Wish I had this knowledge when I was 30. Would have made me a ton more money with a lot less stress.