#1, the shadow on the number plate is distracting, keep an eye on where the light is hitting as half of the front wheel is also in a shadow. the left hand side backround is also distracting, maybe if you had turned the car 45-90degrees to the right and used the hedge as the backround might have helped. also try to leave room for the car to 'drive into', have space infront of the car not behind it for this style of shot.
#2 needs more practice, not a bad attempt but try to shorten your shutter speeds or shoot from further away, again leave space for the car to drive into
#3 get the driver to wear darker clothes and shoot later at night to get some light trails etc into the shot, also could be sharper
#4 watch your reflections in the rear of the car also try to get the car in the backround further out of focus by either larger apature or longer focal range.
these are just my opinions, feel free to ignore all of the above but one thing i have found is totally invaluble for car photography is a poleriser filter, gives images so much extra punch it's unreal!