I'm told mirrors along hallways and such help the signal.
I've never had the need though to test this.
If it's a usb based wireless, I used to have to hang mine near the floor to get the 100% signal. For my one computer I had to add a longer USB extension wire to it.
In my case channel 6 works the best for me, would need to type in your router IP in the address bar to get into the router. Then in wireless settings can change the channel.
If really desperate can buy whats called a "wireless repeater".
You set this somewhere at the halfway mark between your router and wireless devices.