Double Up When Stocks Are Down
Common knowledge for a good way to your long term returns up is to buy when the market is down.

When you manage to see that the long term trend is up it makes sense to buy more when the prices are up. This can be combined with Dollar Cost Averaging. You can double the amount of money invested every month when the investment has fallen by a given amount. For example if the mutual fund has fallen 15% from it’s year high it is possible to double the amount of money you put in every time period. So if one invests $1000 every quarter, you would invest $2000 every quarter when the price is below 15% off the yearly high.

Drawbacks of the method
This is a method suited for saving. If you are not saving, but investing a large sum of money you have to decide to invest it all, or have money in reserve so you can buy when it is down. As with advice 1, some thinks that it is best to invest the total sum, rather than keeping backup capital to be invested in down periods.