How to decrease ping in cs 1 6

Not download anything while playing, play on a server closer to you, things like that  

Also, make sure you're NIC drivers are upto date. When I installed Win 7 a few weeks back, my ping went from 30s to busting limits of the servers I played. Did a driver update from my mobo manufacture, back to the 30s.

On that theme, make sure the firmware for the modem and the router are up to date also.

Along with what everyone else said,

type in console ~

rate 25000
cl_updaterate 101
cl_cmdrate 101

mainly playing on a server near you.

make sure your connection is FAST PATH instead of INTERLEAVED.

(google for more info, your isp can change this setting)