Blake has published 20 tips to speed up your Wi-Fi network. Here are a few:
YOUR WIRELESS NETWORK
Add a Wireless Repeater/Access Point to extend the range of your wireless network. Of course, extending the wireless network without wires is “desirable” – but where possible use a cable, which is dramatically faster and more secure!
NOTE: The Repeater/Access Point should be the same manufacturer as your Router.
You may need to replace your 2.4GHz cordless phones with either a 900Mhz or 5.8GHz style cordless phone due to interference.