Get Better at Playing Counter Strike

This is a page for new people who are just starting or that are really bad at the game and want to improve.

Steps

Practice your aim so that you can actually hit the people that you are playing against. Practice hitting the targets.
Don't waste time playing against bots, they do not provide training for the skills you really want to work on. Try to find a pub with a small amount of players (between 6 and 10 is fine).
Take time to aim and shoot in appropriate areas. Never crouch when fighting in relative close quarters, as this will put your head at hip level, making a much easier head shot for the other players. Only crouch when fighting in very long distance gunfights.
Keep your cross-hairs at head level at all times. At first it may seem awkward, but it greatly reduces the chances of being ambushed around a corner. Learn to judge head height at different distances, and keep your cross-hairs at that point.
Being a part of a good community can help you improve, because of higher level etiquette.

If you're having trouble hitting an opponent, do not move and shoot. Moving while firing greatly decreases your accuracy. Moving left and right decreases your opponents ability to hurt you.
Body armor is more important than weapons. Buy it first, and then guns second. The AK-47 and M4 are the bread and butter weapons of the Terrorist and Counter-Terrorist forces respectively. These weapons provide a solid choice at a reasonable price.
Always aim for the head in prolonged fights. The recoil of your fire will place the bullets at about head level.
Keep covered at all times.
The loud noise of an AK-47 will scare the enemy a little. This may buy you reaction time.

Avoid calling people losers.
Try playing other FPS. It can help.
See Improve Your Skill in Counter Strike for slightly more advanced strategy/information.