You need a static IP

You choose your static IP according to which router you use

Usually the IP's that you have the choice of using are almost the same IP as the router only the last number between 101 and 199. Many routers show what IP's you can use in their settings somewhere.

E.g. If your routers gateway IP is 192.168.2.1 your static IP should be a number between 192.168.2.101 and 192.168.2.199

Just to be safe make a note of your current settings before changing anything, because if you do this wrong then your internet won't work