Differences between the Natural World and the Sim: Unless you have a state-of-the-art motion platform, you won't have the same seat-of-the-pants feel as in the natural world. You can offset this by paying close attention to what you see and hear.
What you see in the sim is completely accurate, but how you see it is different. Because you don't have the peripheral view from the natural world, in the sim it's even more important to look far ahead of the car.
While great strides are being made in the development of steering wheels, shifters, and pedals that provide more natural-world feel, there's still some work to be done. You'll need a little time to adjust to the different feel that controls have in the sim vs. the natural world.
In the virtual world, your sense of speed will be somewhat diminished. You can't drive it like a video game. Instead, it's best to work up to speed gradually. Enter corners a bit more slowly than you think is necessary.