Here are some tips that will help:
* Stop any and all uploads/downloads while playing
- * iTunes
* torrents
* youtube
* downloads of any mp3/movies
* others...
* Check to see if anyone else is using the internet within your house/office/school
* Do regular antivirus/antispyware scans to get rid of these intruders
I hear from a lot of people that they experience lag when playing this game, my first question is normally what are you downloading? The answer is usually "I'm not downloading anything", but after talking to the player for some time I figure out that they are viewing youtube videos/music while playing. Watching youtube IS downloading and it will effect your internet connection.
Another issue is that many people don't understand how technology works which is fine but there is some basic things that you should know.
A) Internet in your whole house is usually shared with one connection, what does this mean? If one person is downloading on one computer it will effect another person on another computer who is trying to play online video games.
B) Internet is shared within your area that you live in, what does this mean? If a lot of people in your neighborhood are heavily downloading stuff from the internet it will effect you in your house. Normally the peak internet hours is lunch time around noon, directly after school when the kids get home from school, around 6pm when the adults get home from work, and the weekends when most people are online. Keep in mind that this will not effect everyone because different people around the world have different types of internet connections but I do know that it definitely does effect me.
Some of these things such as stopping uploads/downloads can be resolved but there is many other issues that you do not have any control over them and unfortunately you can do nothing about it.
Lag/Latency is not the same as performance related issues with older computers, for that information read the other thread viewtopic.php?f=7&t=42.
If other people seem to stop moving around and you are the only one moving then all of a sudden everyone teleports into new positions and there is a bunch of bombs on the screen then you are lagging.
If a player is sliding across the screen and then stops moving and then slides across the screen again then that player is lagging not you.