I always use "limit orders" except possibly for the first stock I bought which was through a stock broker.

Anyway with the Dow being down 942 points at the low today my limit order filled. Now I'm wondering if I set my limit order low enough. The last time I was planning on buying Target, I set my limit too low and never did get the stock. Sept is suppose to be the worst month for the market and only a couple weeks left so didn't want to go too low and miss my chance.

Anyway, is there a rule of thumb on how low to set your limit order below current market price?