Reducing ping or lag when I use my internet?

When I play computer games such as league of legends, my ping shoots up to about 400ms. I believe it to be caused by the Xbox and wii in my household streaming Netflix movies and usage of Wi-Fi on an iPod and iPhone. Is this problem caused by my modem, router, Internet speed, or ISP. Or do I simply just take turns where only one person can use Netflix at a time etc.

As another LoL player: D I feel the frustration: D You should login to your modem and see if you can prioritize traffic only for your computer. Like I have done: p (Don't tell my flatmate lol)

Do you have "QoS" enabled throughout your Network?
This prioritizes packet 'send' function.

You also might want to try this:
Test all your relevant network stats, but pay particular attention to "network buffer measurements" to see what it is.
ICSI Netalyzr: http://netalyzr.icsi.berkeley.edu/
Requires Java, NoScript users can 'temporarily allow berkley… '

The results will give the entire Network, which includes your ISP, so although your router may be just fine, it could be the ISP config's that are mis-adjusted or could be tweaked. Many's the time a person complains to the ISP, and they flatly deny any responsibility, without actually examining their configs.

Yup when multiple device using internet at the same time, the ping time will increase. There are only one connection. Any additional device will increase ping time

what you can do is use a VPN service. It will create a tunnel between your computer and the server, hence provide better ping time