I'm rendering an image where the camera is in front of the car and I want the front of the car to stand out and look big. Right now it looks quite flat. I tried playing with Focal Length and Sensor Size of the Camera but only thing I achieved was that the car was more stretched near the camera. I don't use blender very often so maybe someone who understands this properties better can suggest the solution.
Focal Length is indeed the parameter you want to edit. You have of course to compensate for the distortion with distance to the object.
Has Focal Length decreases the object will look further and further away, the perspective distortion will get larger and larger, and so the objects closer to the camera will appear bigger, and the ones far away will appear smaller,