I always find it useful to go to the settings page of the router and print the page.
You should also ensure that you know the SSID, encryption type and encryption password - this saves having to change the settings on each of your PCs and devices connected wirelessly.
If you have enabled hardware access control on the router you will also need to know the MAC addresses of all PCs and devices that need to connect. Once again the easiest way is to print the page.