Keep in mind that your goal is to complete the a level under the target time to get the cheat, you don't have to kill everyone in the level or get near perfect accuracy. Only spend time shooting anyone who has the potential to either inflict damage on you or make you fail an objective.
Do not take your time, really rush yourself and get your heart beating fast. Remember your goal isn't just to complete all of the objectives, but complete them very fast.
Try to stick to silenced weapons, loud guns and explosions will draw hordes of enemies running toward you in some levels. Use loud weapons only when you have to, for example when a silenced PP7 won't do and you need a submachine gun.
Whenever possible, use strafing techniques. If you hold C-right while putting the control stick up and slightly to the left, or hold C-left while putting the control stick up and slightly to the right, you can run a whole lot faster forward ( facing diagonally). Strafing is necessary for getting some cheats.
Many people don't know this, but the ending cinematic sequence after you beat the level also adds time. So after you finish the level, immediately press start repeatedly, so the animation is barely shown. A couple of seconds can be saved this way.
This strategy might never come in handy for you, but I'll mention it anyways. Explosions and enemy fire to your back can really give you a giant boost forward to help you cut a second or two from your time.
In some levels, every second counts (archive, for
instance). So if you use the tips above (most importantly, strafing) and not make the smalliest error, you might just barely make it under the target time.
This is not necessary, but it is often useful to have a second person time you while playing so you know of your progress. This becomes very helpful in levels where you are really pressed for time.
