General Tips

Use say_team/radio/voice chat to coordinate with your teammates

Use radio commands, or -- better still -- voice chat via a good headset to communicate with your teammates. The radio commands -- or in the worst, case just using the say_team command -- can help organize your team, but there's nothing better than being able to talk directly to your teammates and have them be able to talk back. If you're a serious Counter-Strike player, you should have a microphone and have your voice chat subsystem configured. Consider the difference between using the canned "Enemy spotted" radio chatter and simply saying, "One in the building on the left, and one sniping from the roof on the right." Voice chat can easily turn even a group of intermediate players into a well-oiled killing machine.

Use hud_centerid

Enabling hud_centerid prints the identifying string -- the text that identifies the person currently under your crosshairs and indicates whether they're friend or foe -- just under the center of the screen, instead of in the lower-left corner. This is a far better place for it to appear, since the center of the screen is where your eyes will tend to be looking in the first place. This helps avoid excessive unnecessary eye movements -- concentrate on the center of the screen.