1. Investors can buy when the index tracked by the index fund ends the downward trend and starts the upward trend, and sell when the upward trend ends and starts the downward trend.

2. When buying, investors can buy through allocation or fixed investment to share the cost of positions and spread risks.

3. Buying and selling by valuation, that is, the index fund buys at a low valuation and sells at a high valuation.

4. Target take profit, that is, investors hold index funds and sell them when they reach the target return, for example, the yield reaches 10%.