Find out your router name then search in google "port forward 'your router name' to xbox live(or something similar).
I've done a few routers, some are easier then others. Just manual an I.P Address to your xbox(the internet info that it has set automatically in the xbox, rewrite the same into manual settings), go to your routers homepage(you would type your I.P address into your internet browser, so something like 168.192.1.2) then you are in.
From there:
1. Easiest is DMZ. If your router has it, you type in the Xbox Manual I.P address(if you did it),tick the box and done.
2.Next is UDP and TPP or something. You put in specific numbers to make the xbox NAT go away. All routers i have tried already has the xbox live numbers pre ready in a drop box.
There are probably other ways but those are the ones i know of. Sometimes when you first assign it, the xbox connection can drop out(not always) so stick with it for a day if you manage to get it working.