What type of light will you be using? I'll assume an HID with an air-cooled hood.
- Filter (at the very top of the tent)
- Fan, connected directly to filter, pulling air through the filter
- Ducting to one side of the hood to the fan
- Ducting from the other side of the hood to outside the tent (preferably to outside, or at least another room the tent is in)
If you don't have an air cooled hood, simply Filter->Fan->Outside.
When you first turn on the fan with the filter, do it outside. Some filters expel a bunch of carbon particles on first run.