taken from
http://www.linksys.com/covad/faq.asp
The best place to put your Wireless Router is as close to the center of the area that you want to cover.
The worst place to be (weakest signal) is directly under a Wireless Router.
You'll probably do best if you orient your Wireless Router's antenna(s) vertically.
Keep antenna(s) away from large metal objects like filing cabinets and away from operating microwave ovens or 2.4GHz cordless phones. Also watch out for large containers of water. Fish tanks or water heaters for example.
If you're having trouble with getting a strong signal with your laptop, try moving so that the laptop's wireless card antenna is pointing toward the Wireless Router.
Avoid antenna placement close to an outside wall (unless outside is where you want to be). Also, if you want to connect while you're outside, place the Wireless Router near a window.