Alex, there's actually a reason people aren't being forth coming with answers.
The reason is you provided little to no information, you are receiving equally informative answers. What you may not be aware is, there is no magic remedy. Just code it in a sparingly way. After awhile you may come up with these kinds of optimizations on your own, suited to your specific game.
Perhaps you should start with creating a tick system, for instance, instead of running everything once every ms, (or more without a sleep) - consider executing it once every period of time. Many games use a tick of 33-99 times a second. Then you can start on only processing & sending the data relevant to particular clients.