If your router supports it, enable QoS (quality of service) it will prevent other large packets from having priority over gaming and VOIP. handy to fix this.
However if you have a slower conenction, there is nothing you can do.
Open command prompt (cmd in run) and type "ping -t ip.ip.ip.ip" of whatever server you are wanting see if there is a large fluctuation of time. If there is then it is most likely network, if it's a constant higher number, regardless of the time, then it's your connection.