You must start things off by imagining them. You should know what exactly you are trying to imagine. Make sure that you let your imaginations run wild. Think about the wings, the fans and the shape that you are trying to put into the aircraft/car that you will be making. Be sure that you make it as small as you can because cars have to be on the road while the planes have a totally different shape. Try to make it compact and think about the fact that the flying car you are trying to make has to be on the road, and has the ability to fly as well.
Once you are done with imaging everything, now is your time to draw everything out. Grab a pen and paper and start designing whatever you have imagined. You should be able to differentiate between a car and an aircraft. Try to make it compact and think about the fact that you have to design a car and not a plane. That way you will design the tires and make a car for everyday use.
Once you are done with designing the car on paper, you will know what it should look like in real life. Now is your time to use some clay and put it in a shape of a model. Try to take it as close to the drawn shape of the car as possible. Keep correcting the mistakes that you made on paper and try not to make them when you are making a model. You will be able to make the model in about 4 to 5 hours and during that time keep correcting all the mistakes that you have been making before.
Once you are done with making the model, now is your turn to look at it and spot all the mistakes that have been made in it. Correct them once you are done.
Posted by master-yoda in Cars