You should always ready with a new paper, pencil and eraser.Then first imagine the image of MINI COOPER in your mind or you can use a real image of car either a photo on paper or in mobile phone or in laptop.
Then concentrate the boundary line of image of car. After imagine or seeing the boundary of car you can start the sketching. Making the rough sketch of its boundary using light pencil.
After that identify the sharp corners and edges of image and make it fine using pencil.
Now you have to identify the easier and inner boundary part of car. So please choose the tires for that and completed the Tyre sketch. Now draw the curve part of mirror that are the easy one.