There is a tool or a setting that does this, but I cannot remember. It might be the rule based optimizer. You can check the DBA forum.

The basic idea is that you want to get rid of as much data as soon as possible. I think you know this, so pardon this wordy example.

You want to locate males in a certain city. The city data is distributed across 20 cities with the largest city having 15% of the sample. The sex data is distributed across male and female equally. In this case, you could screen on sex and get rid of 50% of the data where as city may only screen 15%.

The conclusion is that you need to know your data!

Good luck.