To first lower your ping, your going to have to understand what your ping is.
Ping refers to the network latency between a player's computer, called a client, and the game server. This is usually measured in milliseconds. The average ping is in the 100's, anything higher than 200 will make you lag. Low ping is always better than high ping and allows for smoother faster gameplay.
Think of it this way.
Your computer: "Hello Server"
Server: "Hey buddy!"
The time it takes for your message, Hello Server, to reach the server, and then the time it takes for the servers reply is your ping. If you have a bad internet connection your internet may lose a few "packets" of data on the way and your message will be like this
If you lose packets the server will only register the packets it receives and will not fill in the blank. This means if you shoot 30 bullets into an enemy and lose 10 of them in lost packets then only 20 bullets will register even if all 30 hit.
Now that we know how ping will affect your gameplay let's see how we can get it fixed :)
You can use this site to test your ping on the nearest server to you: http://pingtest.net/
Go to your command prompt found in the accsesories section in your start menu and type, for example, "ping www.game-debate.com" (Without the quotation marks). Using this site you can get a estimate on how much ping you will get in an european server.
Now for the important part. The technique for the way of the reducing ping :D
1. Use a modem instead of a router. If you are using a router use the LAN cable instead of Wi-Fi. Never use mobile data connections. (The reasone is signal strenght. When using wireless data connections you might find yourself losing lots of packets of data)
2. Turn off AV and other softwares like Peerblock that will limit network connections. (Since these programs will scan every data packet you recieve you will find yourself hitting a bullet in an enemy ages after shooting)
3. Configure GameBooster to close every unnessasary process and use it. (Running lots of programs in your backgroung will also add some ping) [Download link: http://www.freenew.net/windows/game-booster-3-1/544431.htm]
4. Defrag your HDD often. (This is something you should always do at least once every two weeks)
5. Close your browser. (Watching YouTube videos and staying logged on to your Facebook or GD profile will add to your ping as well)
6. Stop all download processes that will jam your network connection. (Keep all your bandwidth to play the game do waste it on anything else)
7. Join a server which is closest to you. (The further you are from the server the longer it takes to make your kill)
8. Get a better internet connection. (having a faster and more stable connection is always good)