I'm going to repeat what I wrote earlier, re-worded a bit.

Achieving financial independence and then investing during retirement

Phase 1 - Your wealth building years (pre-retirement)

1. Start investing early, preferably in your 20s
2. Live below your means, max out your 401K contributions each year, and allocate 100% of that to an index fund
3. Let that compound and grow tax deferred.
4. Don't get cute and try to time the market. Don't panic sell.
5. Ignore anyone or any article that says the market is "overvalued". They don't know YOUR time horizon. Your time horizon could be 25 years, 15 years, 10 years, 5 years - they don't know.
6. Consistency is key. Keep the index fund investments from your paycheck on autopilot. Yes, it's boring. You don't need drama or excitement to get rich.

Phase 2 - Investing during retirement

7. Once you hit your retirement number, set aside N years of living expenses in cash or cash equivalents. The number N depends on what each person finds comfortable, I recommend 3 to 5 years. The rest can be split between an index ETF and a bond fund. At this point, 4% of your liquid assets should be able to fund your annual living expenses. Consult with a professional financial advisor if you're not sure about how to manage your nest egg.
8. Enjoy your retirement. You've earned it. Don't look at your portfolio every day or every week.

Mechinv
To succeed at investing, your emotional fortitude counts vastly more than your intellectual acumen.