I'm sure the majority of people that played GTA IV don't know about these two.
- While aiming a gun on foot, press the back button or the button that changes the driving camera. It'll zoom out each time to a different distance, gives you more vision around the main character while aiming.
- Press the key or click and hold the right analog stick while on foot, you'll get a camera angle behind the player character. If you have a weapon out, press/click in the button, hold it, and press the aim button. You'll do a 180 degree turn instantly and be facing where you were aiming behind the main character.