In addition to QoS, some routers have the option to give your IP address priority over all other IP's on your network.
But I agree with Arie. QoS in most low end consumer routers is garbage and doesn't worth a damn.
I will tell you that, my "lag" when people are on netflix/youtube etc, has been reduced by about 90%, when I upgraded from a cheap $30 router to a $100 Asus Dual core dual band router with much higher specs. The performance generally so good I've never even bothered to try QoS.
I may be wrong, but I think the amount of RAM and speed of the routers processor has a lot to do with its performance in keeping gaming low latency when there is other heavy network traffic (e.g. streaming).
If you still have problems after messing with a few settings, you may want to think about getting a higher end router if your funds allow.