You'll inevitably get even better as your map knowledge improves, a huge amount of success in CS depends on facing the right spot at the right time - or being in a spot where your opponent won't expect to find you.
Other tips... stand still for just a fraction of a second before firing, as this is how long it takes for your action-based inaccuracy spread to reset. This even applies if you have a shotgun, but isn't so important for pistols.
Also, even if you're still, and crouched, you'll still be subject to a separate system called recoil - bullets will spray in a set pattern every time. Typically, the first 2-5 will be more or less on target, then the next few will veer upwards, and then a half-dozen or so will pool in the same area way above where you're aiming. The recoil pattern resets if you pause firing briefly (more quickly if you're crouched, I think) or when it reaches the end of the pattern. Every weapon has a different pattern, some are harder to master than others.
With some of the more recoily weapons, like the Bizon or the machineguns, you'll generally do better by aiming below the enemy's feet....
