Wireless Hardware
The first step is to actually start out with the correct wireless hardware. At this time there are a variety of wireless standards. Most people will run either wireless B or G networks. Wireless B networks are older, have less range, and offer very limited security. Wireless G products offer better range and security and there are some variants like, Linksys Speedbooster, that offer some modest improvements to G networks. The next wireless standard, sometimes referred to as N wireless, offers significant improvements but is not yet an official standard, so most of the N products are unofficial (or worse non-compliant).
The least expensive wireless network to build at this time is a wireless G network. The router or access-point should support at least WPA security (if not WPA2). Another feature to look for is some type of state packet inspection (SPI) firewall, that helps block out some internet intrusions. Although it is not necessary to match wireless cards and router brands, it is sometimes easier to do so. In this case you will want all wireless cards to at least feature WPA compatibility, and of course be wireless G. If you have some computers with wireless B cards, you should upgrade them.