1. Investors can buy when the index tracked by the broad-based index fund ends its downward trend and sell when it ends its upward trend.

2. Buying and selling by valuation, that is, index funds buy at low valuation and sell at high valuation.

3. Investors can also make a fixed investment operation, that is, by constantly buying and increasing the share of positions, to share the cost of positions and spread risks, and realize the smile curve effect when the fund rebounds.