Combat

Aim at the upper chest

Counter-Strike has positional damage; how much damage a hit does depends on where it lands. Maximum, of course, is the head; normal damage is done to the torso, and considerably less damage is done to the extremities. For example, the AWM is normally a one-shot kill weapon, but an AWM hit to the extremities is not fatal. The best place to aim, therefore, is the mid-to-upper chest; hits will tend to land in the nominal area, thus doing reasonable damage. Given that almost all weapons have significant recoil, the tail end of each burst will land higher than the chest, which will result in a better than average number of headshots. Just like in real combat, you want to aim at the trunk.

Switch to knife or pistol for rapid movement

One's movement speed depends on which weapon is currently readied. Knives and pistols have the least encumbrance; submachine guns have some; rifles have more; and the largest weapons -- the AWM and the Para -- have the most, requiring the holder to move at a slow walk (which has the side benefit of not making much noise). When a player has one of these guns and has to make a quick move, equip your knife or pistol in order to move faster. Switch back to your primary weapon when you reach your destination and continue the fight. Switch to a knife or pistol for fast movement, and then switch back.