How do I get the best wireless connection for my xbox 360 slim?

I'm having a hard time with the wireless connection on my xbox 360 S. I'm able to connect to xbox live just fine. My only problem with the connection is that my xbox isn't getting the full connection that is should be getting and it's causing it to lag and slow down a bit when I'm playing online matches with other people. I look at the internet connection meter on my xbox 360 S and I'm getting only 3 out of 4 bars on it so it's doing alright sorta but still not getting full connection. I know it's not my internet speed because I have road runner turbo and I know it's not my router because I have a netgear N300 dual band router (model WNDR3300). My router and xbox 360 S is both on the opposite side of the house and I have no way possible of being able to move either of them. Plus, my xbox 360 S isn't the only online device in the house either. I was told that a wireless N repeater would work fine to help the connection better and that I should also portforward my xbox 360 S. I don't know what portforwarding is. Would it help if I got a wireless N repeater? Also, can someone explain to me what portforwarding is and how to do it? Thanks a bunch!!