Hi! Well here are a few tips that will help, looking at your channel I notice you do not have custom thumbnails. Get them! People are more likely to click a video if it has custom thumbnails!
Write in your about tab, what you plan on uploading, maybe even a schedule!
Interact with your audience, tweet on twitter! Don't just connect your account then forget about it, tweet people interact with the community so people will follow you!
Set yourself from the rest, what makes your channel different to all the other COD channels? Maybe branch off into other franchises, so you can attract a bigger audience!
Hope these tips helped you, if you need more just asked!
All the best - Turtle