3 rules

1. Keep cash. Don't invest all the money, the market can dive deeper any time.
2. Buy a stock that you've watched for a long time and price has dropped to a support line. Place a limit order that is 5% below the market price, to provide more cushion.
3. Sell put calls that is out of money. Exercise price is 10-20% below the market price. Let time decay work for you.